AGGREGATE RESOURCE INVESTIGATION FOR SELECTED AREAS OF THE SAN PASQUAL BAND OF MISSION INDIANS RESERVATION,
VALLEY CENTER, CALIFORNIA
by
ii
A thesis submitted to the Faculty and the Board of Trustees of the Colorado School of Mines in partial fulfillment of the requirements for the degree of Master of Science (Geological Engineering).
Golden, Colorado Date______________ Signed:_____________________ Eric A. Bergstrom Approved:_____________________ Dr. Jerry D. Higgins Thesis Advisor Golden, Colorado Date_______________ _______________________ Dr. Murray Hitzman Professor and Head Department of Geology and Geological Engineering
iii ABSTRACT
The San Pasqual Band of Mission Indians of southern California requested technical assistance in identifying and assessing geologic resources on their Reservation with respect to their potential for use as crushed rock aggregates. The Reservation is located in the Peninsular Ranges physiographic province in southern California, which is characterized by steep mountains and valleys. The region is underlain by granitic rocks of the Peninsular Ranges Batholith, a composite mass of Cretaceous age rocks emplaced through plutonic intrusion between 122 and 98 million years ago. The target materials were bedrock deposits of gabbroic rock from the Peninsular Ranges Batholith.
Phase one of the study included construction of a GIS database containing geologic, land use, mining, and transportation systems data. The second phase was a reconnaissance geologic mapping and sampling program. This program took advantage of the bare rock exposures uncovered by the fall 2003 Paradise Mountain Fire to map the geology of the Reservation. The samples collected during this program were tested to determine aggregate properties for various geologic units and to identify the best areas for detailed investigation.
Next, a geophysical refraction survey was performed to determine the thickness of the weathering layer overlying buried competent bedrock. The fourth phase was a drilling investigation program to identify subsurface geology properties and collect samples at depth for aggregate properties testing. Findings from the drilling were compared to refraction survey interpretations to construct an accurate geophysical model.
The study area of the San Pasqual Band of Mission Indians Reservation is underlain by the San Marcos Gabbro. This rock unit is buried under a colluvium layer containing hard corestones of gabbro ranging from 15 to 27 feet thick. Gabbro beneath the colluvium is highly to extremely weathered to a depth of at least 70 to 100 feet below
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the ground surface. Hard, fresh San Marcos Gabbro was found in limited surface outcrops but is primarily buried at least 70 feet below ground surface.
Aggregate properties tests indicate that the primary use for the material of the study area would be non-structural fill although some of the material tested meets California Department of Transportation specifications for use as aggregate subbase in road construction. Materials exhibit moderate to high sand equivalent values but low resistance to impact and abrasion. Some of the material exhibits resistance to deformation under load and moderate resistance to water abrasion forces. High quality crushed rock aggregate for use in construction materials such as asphalt or Portland cement concrete pavements exists only at depths greater than 70 feet in the study area.
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TABLE OF CONTENTS
Page
ABSTRACT ... iii
LIST OF FIGURES ... ix
LIST OF TABLES ... xii
ACKNOWLEDGEMENTS ... xiv CHAPTER 1.0 INTRODUCTION 1.1 Introduction ... 1 1.2 Purpose ... 2 1.3 Scope ... 2 1.4 Location ... 3
CHAPTER 2.0 BACKGROUND INFORMATION 2.1 Literature Review... 7
2.2 Geology Introduction ... 8
2.2.1 Regional Geology ... 9
2.2.2 Geologic Units ... 10
2.2.3 Soils... 16
2.3 Local Aggregate Operations ... 18
vi
CHAPTER 3.0 METHODS
3.1 Literature Review and Database Construction ... 19
3.2 Reconnaissance Investigation ... 19
3.2.1 Field Mapping ... 21
3.2.2 Lithologic Examination ... 21
3.2.3 Surface Sampling ... 22
3.3 Geophysics Refraction Survey ... 22
3.4 Drilling Investigation ... 23
3.4.1 Geologic Core Logging... 28
3.4.2 Rock Quality Designation ... 28
3.4.3 Core Recovery ... 29
3.4.4 Weathering Scale ... 29
3.4.5 Strength Scale ... 29
3.5 Sample Testing Program ... 31
3.5.1 Sand Equivalent ... 32
3.5.2 Los Angeles Abrasion ... 34
3.5.3 Sieve Analysis ... 37 3.5.4 Durability Index ... 37 3.5.5 Resistance Value ... 39 3.5.6 Sulfate Soundness ... 40 3.5.7 Specific Gravity ... 41 CHAPTER 4.0 RESULTS 4.1 Literature Review and Database Construction ... 43
4.2 Reconnaissance Investigation ... 44
4.2.1 Lithologic and Petrographic Examination and Geologic Descriptions ... 44
vii
4.2.1.2 Lake Wohlford Granodiorite (Kl, Cretaceous) ... 45
4.2.1.3 Bonsall Tonalite (Kb, Cretaceous) ... 50
4.2.1.4 San Marcos Gabbro (Ks, Cretaceous) ... 53
4.2.1.5 San Marcos Anorthositic Gabbro (Ksa, Cretaceous) ... 54
4.2.1.6 Bedford Canyon Formation (
Ö
bc, Triassic) ... 584.2.2 Reconnaissance Samples ... 61
4.2.2.0 Reconnaissance Sample Los Angeles Abrasion Results ... 61
4.3 Geophysical Refraction Survey ... 68
4.4 Drilling Investigation Results ... 73
4.4.0 Rock Quality Designation ... 76
4.5 Drilling Investigation Samples ... 77
4.5.1 Sand Equivalent Results ... 77
4.5.2 Los Angeles Abrasion Results ... 77
4.5.3 Grain Size Distribution Analysis ... 83
4.5.4 Durability Index Results ... 83
4.5.5 Resistance Value Results ... 87
4.5.6 Sulfate Soundness Results ... 87
4.5.7 Specific Gravity Results ... 87
CHAPTER 5.0 DISCUSSION OF RESULTS 5.1 Previous Studies ... 91
5.2 Reconnaissance Investigation ... 91
5.2.0 Reconnaissance Sample Tests... 92
5.3 Seismic Refraction Survey ... 93
5.3.1 Seismic Refraction Model of San Marcos Gabbro in District C ... 94
viii
5.3.2 Seismic Refraction Model of Lake Wohlford Granodiorite in
District A-2 ... 95
5.3.3 Seismic Refraction Model of Lake Wohlford Granodiorite in District C ... 96
5.4 Drilling Investigation ... 97
5.4.0 Drilling Investigation Sample Tests... 98
CHAPTER 6.0 SUMMARY AND CONCLUSIONS ...101
CHAPTER 7.0 RECOMMENDATIONS ...103
REFERENCES CITED ...105
APPENDICES ... CD in pocket 1. Summit Engineering report results ... APPENDIX A 2. Los Angeles abrasion test data ... APPENDIX B 3. Refraction seismic geophysics survey graphs ... APPENDIX C 4. Geologic core logs ... APPENDIX D 5. Subsurface sample test data ... APPENDIX E
ix
LIST OF FIGURES
Page
Figure 1.1: Location of the San Pasqual Band of Mission Indians Reservation... 4
Figure 1.2: Districts (trust lands) of the San Pasqual Band of Mission Indians Reservation ... 5
Figure 1.3: Aerial photograph of the detailed investigation area and the Lake Wohlford borrow pit ... 6
Figure 2.1: Pegmatite intrusion vein cutting across migmatite in District C ... 12
Figure 2.2: Migmatite xenolith in the Lake Wohlford Granodiorite ... 14
Figure 2.3: Xenoliths of San Marcos Gabbro in the Lake Wohlford Granodiorite ... 14
Figure 2.4: Soils map of the San Pasqual Band of Mission Indians Reservation (modified from Bowman, 1973) ... 17
Figure 3.1: Planned drill hole locations in District C ... 26
Figure 3.2: Photograph of core from drill hole SP-2b ... 27
Figure 3.3: Sand equivalent test measurements ... 33
Figure 3.4: Los Angeles abrasion test equipment ... 35
Figure 4.1: In-situ pegmatite from District C ... 46
x
Page Figure 4.3: Muscovite in thin section SP-1 under cross polarized light from
District C ... 47 Figure 4.4: Lake Wohlford Granodiorite boulders in District C-2 ... 48 Figure 4.5: Biotite from thin section SP-3 shown under plane light on the left and cross
polarized light on the right ... 49 Figure 4.6: A shattered quartz grain in thin section SP-3 under cross polarized light .... 50 Figure 4.7: Bonsall Tonalite hand sample at the outcrop it was collected from ... 51 Figure 4.8: Chlorite alteration along cleavage planes of a biotite grain under cross
polarized light from thin section SP-5 ... 52 Figure 4.9: Plagioclase grains enclosed in a pyroxene grain under cross polarized light
from thin section SP-6 ... 53 Figure 4.10: Samples of the San Marcos Gabbro in District C ... 54 Figure 4.11: Pyroxenes and plagioclase from thin section SP-10 displaying slight
weathering around the edges of the grains under cross polarized light ... 55 Figure 4.12: Euhedral hornblende crystals next to plagioclase under cross polarized
light from thin section SP-12 ... 56 Figure 4.13: Collecting hand samples from the San Marcos Anorthositic Gabbro in
District C ... 57 Figure 4.14: Twinned plagioclase with minor pyroxene from thin section SP-9 under
cross polarized light ... 58 Figure 4.15: Outcrop of the quartzite of the Bedford Canyon Formation ... 59 Figure 4.16: Quartz and potassium feldspar (microcline) crystals under cross polarized
light from thin section SP-8 ... 60 Figure 4.17: Muscovite and quartz grains from thin section SP-8 under cross polarized
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Page
Figure 4.18: Reconnaissance sample locations ... 62
Figure 4.19: Reconnaissance samples collected from District A-2 ... 63
Figure 4.20: San Marcos Gabbro reconnaissance sample locations ... 64
Figure 4.21: Los Angeles abrasion results from the reconnaissance samples ... 66
Figure 4.22: Los Angeles abrasion results from the San Marcos Gabbro reconnaissance samples ... 67
Figure 4.23: Seismic refraction survey locations ... 69
Figure 4.24: Interpretation of velocity zones in the subsurface from seismic refraction survey SPS2 in District C ... 71
Figure 4.25: Interpretation of velocity zones in the subsurface from seismic refraction survey SPS5 in District A-2 ... 72
Figure 4.26: Core of fresh San Marcos Gabbro from drill hole SP-3 ... 74
Figure 4.27: Core of colluvium derived from San Marcos Gabbro from drill hole SP-2 ... 75
Figure 4.28: Core of highly weathered San Marcos Gabbro (24.5 to 35 feet) and San Marcos Gabbro weathered to saprolite (35 to 48.5 feet) from drill hole SP-2b ... 75
Figure 4.29: Sand equivalent results for the drilling investigation samples ... 80
Figure 4.30: Los Angeles abrasion results for the drilling investigation samples ... 82
Figure 4.31: Grain size distributions for the drilling investigation samples ... 84
Figure 4.32: Durability index results for the drilling investigation samples ... 86
Figure 4.33: R-Value results for the drilling investigation samples ... 88
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LIST OF TABLES
Page
Table 3.1: GIS database information sources ... 20
Table 3.2: Drilling plan details ... 25
Table 3.3: Relative scale of weathering ... 30
Table 3.4: Relative scale of strength ... 31
Table 3.5: Sand equivalent specifications (minimum values) ... 34
Table 3.6: Los Angeles abrasion test specifications (maximum values) ... 36
Table 3.7: Sieve sizes used for grain size distribution analysis ... 38
Table 3.8: Durability index specifications ... 39
Table 3.9: R-Value specifications (minimum values) ... 40
Table 4.1: Mineral compositions from thin sections SP-1 and SP-2 ... 47
Table 4.2: Mineral compositions from thin sections SP-3, SP-4, and SP-7 ... 49
Table 4.3: Mineral compositions from thin sections SP-5 and SP-6 ... 52
Table 4.4: Mineral compositions from thin sections SP-10, SP-11, and SP-12 ... 55
Table 4.5: Mineral composition from thin section SP-9 ... 57
Table 4.6: Mineral composition from thin section SP-8 ... 59
xiii
Page
Table 4.8: Refraction survey interpretation data... 70
Table 4.9: Field drill hole location information ... 74
Table 4.10: Drill hole RQD summary... 76
Table 4.11: Depth interval and tests performed on drilling samples ... 78
Table 4.12: Sand equivalent test results from the drilling investigation samples ... 79
Table 4.13: Los Angeles abrasion test results from the drilling investigation samples ... 81
Table 4.14: Durability index test results from the drilling investigation samples ... 85
Table 4.15: Sulfate soundness test results from the drilling investigation samples... 89
xiv
ACKNOWLEDGEMENTS
I would like to thank my advisor Dr. Jerry Higgins for his invaluable advice on this project and Dr. Paul Santi for serving on my thesis committee. I would also like to thank the Indian Affairs Division of Energy and Mineral Resources Management
Division Chief Stephen Manydeeds and project managers John Zeise and Erik Ronald for their help and advice.
This project would not have been possible without funding from the Indian Affairs Division of Energy and Mineral Resources Management. Additionally, I would like to acknowledge Melvin Chamberlain of the Operating Engineers Training Trust of Southern California. I also acknowledge Rob and Mike Reedy, Tony Albright, and Scott Zelez from Boart Longyear for providing information and help to the project.
I would also like to thank Curtis Hofmann, Don and Cheryl Calac and the San Pasqual Band of Mission Indians for the opportunity to work on this project.
CHAPTER 1.0
INTRODUCTION
1.1 Introduction
The San Pasqual Band of Mission Indians requested technical assistance from the Indian Affairs Division of Energy and Mineral Resources Management (DEMRM) for assessment of potential aggregate resources on their Reservation. The reservation is located approximately 35 miles from the San Diego urban corridor and approximately 110 miles from the Los Angeles urban corridor (Figure 1.1).
Kohler (2002) estimated the demand for aggregates for these two urban areas over the next 50 years to be 1.1 billion tons for San Diego and 4.5 billion tons for Los
Angeles. The permitted aggregate resources of 0.3 billion tons for San Diego and 1.7 billion tons for Los Angeles (Kohler, 2002), falls significantly short of the projected demands and creates a potential market for aggregates supplied from the San Pasqual Band of Mission Indians Reservation (SPBMIR).
Due to the potential for business development for the Tribe, including
employment, land development and economic benefits, the DEMRM provided funding and technical support for the project. This report and the associated research were completed by a Colorado School of Mines (CSM) Master of Science candidate.
1.2 Purpose
The purpose of the study was to identify potential aggregate resources on the SPBMIR. The specific objectives of the study were to 1) define the geology and aggregate properties of material (primarily decomposed granite) in the area of an
abandoned borrow pit (Lake Wohlford Borrow Pit, figure 1.3); 2) conduct reconnaissance geologic mapping, surface sampling, and aggregate quality testing of materials from selected districts of the SPBMIR; and 3) conduct a detailed investigation of potential sources of crushed rock identified from the reconnaissance work.
1.3 Scope
The project scope included compiling relevant geologic information for the area followed by identifying geologic resources with respect to potential mining products based on material testing. The study was conducted in four phases. The first phase built a geographic information systems (GIS) database for the Tribe from existing geological and geographic information. The second phase of the investigation consisted of reconnaissance geologic mapping and surface sampling. The geology was mapped through observing bedrock outcrops. Surface samples were collected and used in preliminary aggregate quality testing.
The third phase of the project was a seismic refraction geophysical survey. This phase of the investigation explored the thickness of the weathered zone overlying
bedrock. The final phase of the investigation was exploration drilling of gabbro deposits. The drilling provided access to subsurface samples for geologic description and
1.4 Location
The SPBMIR is located in southern California in the Merriam Mountains to the northeast of Escondido, California (Figure 1.1). The reservation spans approximately 1,380 acres (Ritchey and others, 1982) set out in five districts (Figure 1.2). These Districts are named A, A-2, B, C, C-2 as per Tribal convention.
The SPBMIR is contained on the hill slopes around Woods Valley with Bear Ridge passing through district C of the reservation. District C-2 and District A-2 are characterized by very steep slopes while the remainder of the SPBMIR is characterized by lower mountains and ridges. The Lake Wohlford borrow pit is located in district A-2 of the SPBMIR (Figure 1.3). The Reservation is accessible by North Lake Wohlford Road or by San Diego County Road 6 (Valley Parkway). Nearby towns include Valley Center, Escondido, and San Marcos.
Pala La Jolla Pauma Barona Capitan Grande Rincon Pechanga Mesa Grande Santa Ysabel San Pasqual I1 5 S78 S76 S79 S 6 7 I80 5 Poway Ramona Escondido San Marcos
Explanation
San Pasqual Reservation
Other California Indian Reservations Local Cities Highways 0 1 2 4 Miles
±
Riverside County Imperial County San Diego CountySan Bernardino County
Oceanside San Diego San Pasqual Mexico Southern California Merriam Mountains
Figure 1.3 Aerial photograph of the detailed investigation area and the Lake Wohlford borrow pit. The photograph was taken in the spring of 2004.
CHAPTER 2.0
BACKGROUND INFORMATION
2.1 Literature Review
Previous research for the region of the SPBMIR includes reports describing regional geology for the area and geotechnical studies performed for the San Pasqual Band of Mission Indians. Sources included DEMRM, California Division of Mines and Geology, San Diego Association of Geologists, and the San Pasqual Band of Mission Indians Planning Department.
Merriam (1954) mapped a portion of the Peninsular Ranges Batholith (PRB, formerly known as the Southern California Batholith) which includes the SPBMIR. This map sheet is the most comprehensive geologic map of the area. The map was digitized into the database for field use when performing geologic mapping. Merriam also discussed the emplacement of the PRB.
McNary and others (1987) produced an initial mineral resource assessment for the SPBMIR. The report discusses gemstone and metallic ore mining as well as sand and gravel deposits and geology. The report indicates few alluvial deposits on the Tribe’s lands but does not include deposits suitable for crushed stone or specific test results.
Glynn (2000) produced Summit Engineering’s geotechnical investigation of district C with respect to placement of a casino facility. The report features geological descriptions, shallow borehole information, and material testing. The borehole locations
were digitized into the database for reference and were used to plan the subsurface investigation.
Walawender (2000) compiled a book on the geology of San Diego county back country. This is an extensive discussion of the PRB including units and emplacement. The information from the book helped interpret the geology found in the field.
Ulibarri (2001) wrote the environmental assessment for a proposed casino facility in district C. The assessment discusses the soils, bedrock, and tectonics of the area. The report mentions the applicability of processing gabbro from the building location into aggregate usable in the construction.
Kohler (2002) compiled the most recent report on the uses and demands for aggregate across the state of California. It includes a map showing estimates of supply and demand for aggregate consumption areas. The report indicates increasing usage of aggregate in the state and potential shortfalls in permitted aggregate sources. The information from this report was used to determine a market potential for aggregate materials found on the SPBMIR
2.2 Geology Introduction
The SPBMIR is located in the Merriam Mountains in the Peninsular Ranges physiographic province of southern California. The Peninsular Ranges contain northwest-southeast trending mountain ranges with steep valleys. The province is underlain by the PRB, across portions of Riverside, San Diego, and Imperial counties and extending south into Mexico. The total area underlain by the PRB is roughly 49,000 square miles (Todd and Shaw, 1980).
The PRB consists of a composite mass of late Mesozoic intrusive rocks ranging in composition from granite to gabbro (Merriam, 1954). Rock types of the PRB located in the SPBMIR include tonalite, granodiorite, and gabbro (Plate A). Tonalite is a light
colored felsic rock containing plagioclase, quartz, biotite, and mafic minerals such as hornblende, orthopyroxene and clinopyroxene. Granodiorite is a light colored felsic rock that contains plagioclase, quartz, potassium feldspar, and biotite. Gabbro is a dark colored mafic rock containing plagioclase, hornblende, orthopyroxene, clinopyroxene, and
occasionally olivine.
2.2.1 Regional Geology
The regional rock types that were in place before the emplacement of the PRB are metamorphic rocks such as quartzite and schist that are found in small masses throughout the PRB. These metamorphics are inferred to be older than the PRB, approximately Triassic in age, because xenoliths (remnant inclusions of an older rock in a younger rock) of the metamorphic rocks are often found included in PRB rocks (Walawender, 2000).
The PRB formed in a volcanic arc environment involving the subduction of oceanic crust under the continental crust of California (Silver, Taylor, and Chappell, 1980 and Walawender, 2000). The subducting crust heated up to the melting point underneath the continental crust. Then the melted magma moved up under the continent to form large rock masses under the surface without volcanic eruption (although extrusive volcanic rocks are observed several miles west of the study area).
This interpretation is supported by the abundance of amphibole, in this case, hornblende, a hydrous (water-bearing) mineral, found in the PRB (Walawender, 2000). Water trapped in the subducting crust becomes part of the magmatic melt and allows the formation of minerals such as hornblende that require water. If the melt were formed without a source of water, then the mineral assemblage found in the resulting rocks would be approximately the same but would not include hornblende.
The PRB was emplaced approximately 122 to 90 million years ago (Ma). The sequence of rock formation is generally considered to be from mafic to felsic or from
gabbroic rocks through tonalite and granodiorite to granite (Todd and Shaw, 1980). This sequence probably occurred through repeated melting, intrusion, and cooling cycles. As magma cools, mafic minerals such as olivine, pyroxene and hornblende form first. After these minerals have formed, the magma has a high concentration of felsic minerals such as quartz, potassium feldspar, and plagioclase. This sequence was likely aided by repeated infusions of rising magma that would include partial melting of existing
gabbroic crust. The average composition of the PRB is tonalitic in composition, primarily plagioclase and quartz with some mafic minerals, as suggested by the large areas
underlain by tonalite throughout the PRB (Walawender, 2000).
The processes that formed the PRB are considered to have ended roughly 90 Ma (Walawender, 2000). Once the rocks forming the PRB were exposed at the surface they began weathering, reducing the fresh, hard granitic rocks to ‘decomposed granite’, a granitic rock that has undergone weathering such that it easily breaks down to gravel, sand or smaller material.
While no references to specific faults in the SPBMIR were located, the Elsinore fault zone is approximately 25 miles to the northeast. The Elsinore fault zone trends northwest to southeast across San Diego County and has a likely maximum earthquake magnitude of 7.4 (Ulibarri, 2001).
2.2.2 Geologic Units
The geologic units of the SPBMIR include Quaternary alluvium, Cretaceous Pegmatite, Cretaceous Lake Wohlford Granodiorite, Cretaceous Bonsall Tonalite, Cretaceous San Marcos Gabbro, and Triassic Bedford Canyon Formation (Plate A). Several of the units display an east to west trend; the primary rock type of the northern portion of the reservation is the Bonsall Tonalite, while the primary rock type of the southern portion of the reservation is the Lake Wohlford Granodiorite. The Bedford
Canyon Formation is also oriented east to west but displays more variation in the direction of the contacts. The San Marcos Gabbro is comprised of two irregular shaped masses in the southern portion of the SPBMIR and is likely the remnant of a larger mass (Merriam, 1954). The east to west trend displayed in the region of the SPBMIR is a localized occurrence, as the regional map produced by Merriam (1954) does not show this feature anywhere else.
The Quaternary alluvium (Qal) is primarily gravelly sand with clay and silt. This unit is located in the lower elevations of Bear Valley and Woods Valley. The light tan to grey sand, silt, and clay is derived from the Lake Wohlford Granodiorite and the Bonsall Tonalite. The dark red clay is derived from the San Marcos Gabbro. The thickness of the alluvium is estimated to be at least five feet (Bowman, 1973).
The Cretaceous Pegmatites (Kp) are light colored intrusive rocks with crystals up to one foot in length of quartz, plagioclase and potassium feldspar (Figure 2.1).
Muscovite, epidote and tourmaline (schorl) are also present in lesser amounts in the pegmatites. Epidote and schorl samples displayed well developed rod shaped crystals up to 1 ½ inches (3.8 centimeters) in length. The pegmatites form small intrusive bodies that are two inches wide up to several feet wide (3 centimeters to 1 meter) and several feet up to over 200 feet long (1 to 61 meters). The pegmatites identified in the field are areas with concentrations of quartz, plagioclase, and potassium feldspar rocks embedded in the soil (float). Outcrops of the pegmatites are rare in the SPBMIR study area.
The Cretaceous Lake Wohlford Granodiorite (Kl) is a light tan with orange rock that underlies an area extending from several miles east of the SPBMIR to west of the SPBMIR near Escondido and from the north part of district C to the south part of district C-2 of the SPBMIR including all of district A-2, roughly 8 square miles in size. The age of the formation is approximately 102 to 109 Ma. The unit typically forms rough, craggy mountains with boulder-strewn slopes (Jahns and Wright, 1951). The highest elevations of the SPBMIR, roughly 2300 feet above mean sea level, are underlain by the Lake Wohlford Granodiorite. Minerals observed in the Lake Wohlford Granodiorite include
quartz, potassium feldspar, plagioclase, and biotite. Crystal sizes range from one to five millimeters.
Figure 2.1 Pegmatite intrusion vein cutting across migmatite in district C.
The unit has weathered to decomposed granite at the surface resulting in corestones (less weathered boulders) left on the surface after the material surrounding them has undergone chemical weathering and decomposition to sandy soil. The thickness of the soil cover could not be determined in the field.
There are many xenoliths of migmatite and San Marcos Gabbro up to 20 feet (six meters) in size observed in the Lake Wohlford Granodiorite in district C. The migmatites
may have originally been part of the Bedford Canyon Formation and contain grey biotite schist with pink veinlets of quartz and potassium feldspar (Figure 2.2). The migmatite formed through partial melting of muscovite in the biotite schist which re-crystallized into veinlets in the remaining biotite schist (Walawender, 2000).
The xenoliths of San Marcos Gabbro are black to reddish black, ellipsoidal inclusions in the light colored granodiorite (Figure 2.3). The shape and preferred orientation of these features suggests that they are solid rock fragments that were incorporated into the granodiorite when it was emplaced (Walawender, 2000).
The Cretaceous Bonsall Tonalite (Kb) (called blue granite locally) is a white and black rock which is the most widespread unit of the PRB with ages varying from 102 to 109 Ma (Walawender, 2000). The formation is exposed on rough, craggy mountains with boulder-strewn slopes which are less steep and lower in elevation than mountains
underlain by the Lake Wohlford Granodiorite, suggesting a lower resistance to erosion in the tonalite. The tonalite is composed of plagioclase, quartz, hornblende, magnetite, orthopyroxene, clinopyroxene and biotite. Crystal sizes range from one millimeter up to four millimeters. The rock is weathered to decomposed granite at the surface with corestones similar to the Lake Wohlford Granodiorite. The thickness of the soil around the boulders is unknown; however, observation of road cuts in the area suggests that the soil cover may be as thick as 25 feet (eight meters) in some areas.
The Cretaceous San Marcos Gabbro (Ks) ranges in composition from an
anorthosite to a gabbro with the majority having a gabbroic composition (Rogers, 1965). The gabbro is a dark gray to black rock often with a red or orange coating found in small masses throughout the PRB varying in age from 109 Ma to 122 Ma, the oldest rock type of the PRB (Walawender, 2000). The San Marcos Gabbro typically forms smooth, regular slopes covered with a mantle of dark red clay soil (Jahns and Wright, 1951). The unit is composed of plagioclase, hornblende, magnetite, orthopyroxene, clinopyroxene, pyrite, and olivine with crystals from aphanitic (not visible to the naked eye) to two millimeters in size.
Figure 2.2 Migmatite xenolith in the Lake Wohlford Granodiorite, scale card is six inches.
Figure 2.3 Xenoliths of San Marcos Gabbro (Ks) in the Lake Wohlford Granodiorite (Kl), scale card is six inches.
Kl
The gabbro is extremely weathered at the surface. Slopes underlain by the gabbro are covered by a layer of colluvium (Qc). The colluvium consists of red clayey, silty sand with corestones of San Marcos Gabbro and Lake Wohlford Granodiorite. The corestones are several inches to two feet (1 to 60 centimeters) in diameter as observed on the surface and are very strong (Table 3.4). The bedrock beneath the colluvium is San Marcos Gabbro that is highly to extremely weathered including some that has weathered to saprolite (Ksw). A saprolite is defined as disintegrated and decomposed rock with soil-like properties but the fabric and structure of the rock is preserved. Core samples of this saprolite have the appearance of the surface boulders but crumble easily under finger pressure or if handled.
The San Marcos Anorthositic Gabbro (Ksa), a small body found in the San Marcos Gabbro, has a salt and pepper appearance that resembles the Bonsall Tonalite. This unit forms a boulder-strewn hill in District C. The anorthositic gabbro is composed of plagioclase, orthopyroxene, clinopyroxene, and hornblende. Crystal sizes range from one millimeter up to three millimeters. The boulders at the surface are slightly weathered and break into flaky chips under impact from a sledgehammer. The unit was formed during the emplacement of the gabbro pluton when the melt was cooling. The darker mafic minerals tend to crystallize early and sink towards the bottom of the magma chamber. This leaves a melt towards the top of the chamber that is more enriched in plagioclase. Walawender (2000) suggests that gabbroic rocks of the PRB that are rich in plagioclase probably indicate the top of an ancient magma chamber.
The Bedford Canyon Formation (
Ö
bc) is comprised of two units, quartzite and schist. The quartzite is a pink, red, and tan rock while the schist is a black, aphanitic, vitreous rock. The quartzite is very resistant to weathering and typically forms narrow ridges with many outcrops. The quartzite is composed of quartz, potassium feldspar, muscovite, and biotite. The schist is not resistant to erosion and is typically found in valleys and streambeds. Biotite was the only mineral identified in the schist due to theaphanitic grain size. Crystal sizes in the quartzite range from one to three millimeters. The quartzite is slightly weathered (barely breakable under impact from a sledgehammer) while outcrops of the schist are moderately to extremely weathered (break easily under impact from a rock hammer). Tight folds were observed in the quartzite unit. The folds imply that the unit has been deformed plastically in the past.
2.2.3 Soils
There are nine primary soil families identified in the area by the soil survey (Figure 2.4) (Bowman, 1973). Acid igneous rock land is the largest soil group in the study area and it contains no sub groups. This soil consists of the areas of the reservation that are covered in rock outcrops and rounded granitic boulders. There is no estimate on the thickness of this unit.
The Cieneba, Placentia, Ramona, and Visalia groups are all soils derived from granitic rocks or granitic alluvium. The groups formed primarily from the weathering of the Lake Wohlford Granodiorite and secondarily from the weathering of the Bedford Canyon Formation and the Bonsall Tonalite and are common in Districts C-2 and A-2 of the reservation. The soil survey only describes the thickness of soil up to 60 inches (five feet), so the thickness of these soil groups was estimated to be greater than five feet.
The Fallbrook and Vista groups are derived from granodiorite and tonalite materials. Both groups are the weathering products of the Bonsall Tonalite with very minor contributions from the Lake Wohlford Granodiorite and are most found in Districts A and B of the reservation. The thickness of these soils is greater than five feet.
The Las Posas soil family is composed of material weathered from basic igneous rocks. It is derived from the San Marcos Gabbro with minor contributions from the Lake Wohlford Granodiorite and is a dark red clayey and silty material found in district C of the SPBMIR. The thickness of this soil is greater than five feet.
V a B L rG C m rG Ac G C n G 2 F v E V a A C n G 2 Ac G F a E 2 Ac G L rE C m rG F v E F a C 2 C n E2 F a C 2 L p D 2 V a B Vs C C m E2 C m rG C m rG F v D L p D 2 Vv D R a D 2 L rG V a B C n E2 C m E2 F a D 2 F a D 2 Vs E 2 V a B L p E2 L p C 2 Pe C V a C L p D 2 F a D 2 F a C 2 L rE V a B L rE Vv D C m E2 V a B Bl C 2 Vs E Vs E 2 L p D 2 F a E 2 Bl D 2 Vs C Bl C 2 Vv E V a D F a C 2 R a D 2 V a C F a D 2 F a D 2 Vs D V a B Vs D L p D 2 C m rG V a B Vv G V a B E xp lan ati o n S a n P a s q u a l In d ia n R e s e rva ti o n A ci d I g n e o u s R o ck L a n d B o n sa ll S e ri e s C ie n e b a S e ri e s Fa ll b ro o k S e ri e s L a s P o sa s S e ri e s P la ce n ti a S e ri e s R a m o n a S e ri e s V isa li a S e ri e s V ist a S e ri e s 0 2 ,0 0 0 4 ,0 0 0 1 ,0 0 0 F e e t
±
F igure 2.4 S oil s map ofthe San Pasqua
l B and of Mi ssi on In dians Rese rva tion (modifie d fr om B owma n , 1973) .
2.3 Local Aggregate Operations
Local aggregate operations observed in the field include two major aggregate operations nearby the SPBMIR. Both operations are north approximately 15 to 17 miles from the reservation along California highway 76.
The Calmat Pala Aggregate Mine is operated by Vulcan Materials and is located within the Pala Indian Reservation. The operation is primarily sand and gravel mined from the alluvial slope surrounding Magee Creek, although crushed rock may also be a product from the pit. Facilities include a concrete batching plant and an asphalt mixing plant.
The Fenton Sand Mine is operated by Hanson Materials Pacific Southwest and is located two miles north of the Pala Indian Reservation. The pit mines sand from the bed of the San Luis Rey River.
2.4 Description of the Lake Wohlford Borrow Pit
The Lake Wohlford Borrow Pit is located in district A-2 (Figure 1.3). The disturbed area is roughly 210 feet wide by 370 feet long, about 1 ½ acres. The disturbed area is characterized by steep slopes covered with pea gravel sized weathered
granodiorite from the Lake Wohlford Granodiorite.
Very little information remains on this small pit. It is unknown what company ran the operation, exactly when it was opened and when it was closed, or the quality of the material mined. From conversations with Curtis Hofman, with the Tribal Housing Planning Department at the time, material from the pit was mined using a bulldozer with ripping techniques and was used as road fill on the SPBMIR.
CHAPTER 3.0
METHODS
3.1 Literature Review and Database Construction
Library, internet, and Tribal resources were reviewed to develop a GIS database. The database was compiled utilizing ArcGIS software produced by the ESRI
Corporation. Existing digital information collected included digital aerial photographs, digital raster graphics of topographic maps, reservation boundaries, county and state boundaries, roads, rivers, and canals. Hard copy information that was digitized for use in the database included regional geologic maps, large scale topographic maps, and location of boreholes from Glynn (2000). The information sources are described in table 3.1.
The database was used in planning the field investigation including access points for the reservation, estimates of mountain slope gradient, and locations of developed areas. Aerial photograph information and geologic information combined with input from the Tribe was used to select the Districts targeted for the next phase of the investigation.
3.2 Reconnaissance Investigation
The field investigation for San Pasqual consisted of reconnaissance level geology and surface sampling. The geologic investigation included identifying units, examining hand samples and thin sections, and creating a geologic map. Surface samples were collected for aggregate quality testing. The field observations and the testing results were examined to narrow the focus of the geophysical refraction survey phase of the study.
Table 3.1
GIS database information sources.
GIS data layer description Estimated reliability of source Pixel size (if relevant) Source Reservation boundaries, state and county boundaries, roads, rivers, canals High DEMRM Digital orthophoto quadrangles
High 5 meters California Spatial Information Library, http://casil.ucdavis.edu/casil/usgs.gov Digital raster graphics of USGS topographic maps
High California Spatial Information Library, http://casil.ucdavis.edu/casil/gis.ca.gov/drg/
Aerial photographs (post 2003)
High 1 meter San Diego GIS Organization
http://www.sangis.org
5469 Kearny Villa Rd, Ste 102, Ste 130A San Diego, CA 92123
3.2.1 Field Mapping
Geologic mapping was conducted during two field trips. During the first trip the geology of the Lake Wohlford Borrow Pit (Figure 1.3) was mapped along with rock outcrops of other geologic units. Geologic boundaries from existing geologic maps were checked in the field but mapping was restrained due to limited road access and
impenetrable scrub brush. The second mapping trip was undertaken after the 2003 Paradise Mountain Fire which revealed many rock outcrops previously inaccessible. The better access allowed mapping of geologic details such as pegmatites, mineralogical rock changes and geologic boundaries (Plate A). Hand samples were collected from rock outcrops to supplement geologic unit descriptions.
3.2.2 Lithologic Examination
The lithologic examination was a description of the minerals composing the rock units in the study area to supplement the geological descriptions of the units. This process identified high quality aggregate minerals (quartz, plagioclase, etc.), low quality
aggregate minerals (pyrite, biotite, etc.), and mineralogic features of the rock (grain angularity, average grain size, weathering features, etc) that control aggregate quality. The resulting lithologic descriptions were written following guidelines from Santi (2002). Both hand samples and thin sections were examined. Twelve thin sections were prepared at the Colorado School of Mines to represent the rock types found across the reservation. Each of these thin sections was examined under a Nikon petrographic microscope and the results were compared with observations from the corresponding hand samples. Mineral percentages and mineral weathering from the thin section observation supplemented unit descriptions.
3.2.3 Surface Sampling
Surface samples were collected from rock outcrops and corestones for aggregate properties testing as described in section 3.6. Samples were collected using a
sledgehammer and chisel to collect cobble sized material. The samples were transported in five gallon buckets.
3.3 Geophysics Refraction Survey
A seismic refraction survey was conducted to determine the thickness of
unconsolidated materials as well as the depth of the weathered zone overlying bedrock. Seismic refraction is based on the refraction of seismic waves from subsurface units. An energy source is provided at the surface, a sledgehammer in this case, which sends waves through the ground. Geophones detect the waves and the travel time of the waves is recorded at each geophone station. Interpretation of the travel times provides material information because waves travel faster through a subsurface unit such as bedrock than they do through upper unconsolidated material. The depth of the unit with the higher velocity can be estimated using the travel time interpretation.
The equipment used was a Stratovisor NX collection system utilizing 30 or 55 channels with geophones spaced six feet (two meters) apart. Survey lines were 330 feet (100 meters) in length or 180 feet (55 meters) in length. The 330 feet long lines were estimated to be able to detect features to a maximum depth of 105 feet (32 meters), one third of the line length (Redpath, 1973) while the 180 feet lines were estimated to be able to detect features to a maximum depth of 67 feet (20 meters). Longer survey lines were utilized where allowed by topography; otherwise the shorter survey lines were used.
For each geophone spread, the geophones were placed in a straight line. The refraction energy source was a 16 pound sledgehammer struck against a steel plate.
Refraction data was collected every 30 feet (nine meters) along the length of the survey line. In addition data was collected from points 30, 60, and 90 feet (9, 18, and 27 meters) before the first geophone and after the last geophone to supplement interpretation of the features at the beginning and end of the survey line.
The refraction data collected was interpreted and modeled using the Millenium Software package produced by Green Mountain Incorporated. This software is used to pick first breaks, determine velocity breaks in slope, calculate material velocities and delay times, and model the thickness of velocity zones. Differing velocity zones generally indicate a change in subsurface materials. Millenium uses an assumed value for the velocity zone of the unconsolidated material from the surface to the first significant change in velocity. The assumed velocity used for the soil cover of the SPBMIR was 3,000 feet per second (900 meters per second) which is in the range for unconsolidated surface material (Redpath, 1973). The depth below ground surface to the significant change in velocity is modeled to provide an interpretation of the thickness of weathered material overlying bedrock.
3.4 Drilling Investigation
The drilling investigation was designed to provide information on the thickness of the weathered zone overlying the San Marcos Gabbro and to provide samples of
unweathered rock from depth for aggregate properties testing. The initial design included drill holes in District A-2 and District C but the drill holes planned for District A-2 were abandoned as discussed in section 4.4. The investigation design was based on information from the database, the literature, and the resource model and was modified during the drilling to accommodate new information discovered while drilling.
All the drill holes were planned at a 45 degree angle allowing horizontal travel of the drill while still being able to recover the core using gravity. The angled drill holes were chosen over using vertical holes for the following reasons:
Geologic contacts between units in the area were assumed to be vertical and angled holes increased the chances of intercepting these features.
Boreholes from the Glynn (2000) study were vertical and, since the boreholes were in the same area as the drilling investigation (Plate B), it was decided not to duplicate the work.
Pegmatite orientation in the area of the drilling investigation was observed to be straight downhill and the drill holes were angled in order to verify the presence of the pegmatites at depth.
Table 3.2 is a listing of the planned drill hole orientations and depths while Figure 3.1 is a map of the planned drill hole locations. The azimuth of orientation is the
clockwise angle from north for each drill hole (for example an orientation of 90 degrees means a hole drilled towards the east, an orientation of 180 degrees means a hole drilled towards the south).
Drilling services were provided by Boart Longyear with a Longyear 44 rig driving HQ diameter core (2 ½ inches inner diameter). Existing access roads were used after improvements and drilling pads were constructed by the Operating Engineers Training Trust of Southern California.
Table 3.2: Drilling plan details.
2004-2005 Exploratory Drilling Program
San Pasqual Indian Reservation, Valley Center, California
Drillhole ID Azimuth of Orientation Estimated Depth (Ft) Surface Elevation (Ft) DH-1 225 70 1885 DH-2 135 160 1968 DH-3 45 100 2120 DH-4 90 100 1945 DH-5 135 100 1950 DH-6 315 80 1950
Preliminary Total Length: 610 Feet Note: All drillholes are inclined 45 degrees.
Note: Drillhole depths and locations are based on preliminary investigation and may be revised in the field based on discoveries during drilling.
DH4 DH1 DH5 DH3 DH2 DH6 1950 1 9 2 5 19 00 19 75 2 0 0 0 20 25 1875 18 50 205 0 1825 2075 1800 1775 2100 1750 17 25 21 25 1700 2150 1 6 7 5 20 5 0 1775 Kl Ks Ksa Kl Kl Kp Kp Kp Kp Kp Kp Kp Kl Ks Kl
±
0 100 200 Feet ExplanationPlanned Drillhole Locations
DHID, Orient, Dip, Depth
DH1, 225, 45 Depth 70 ft DH2, 135, 45 Depth 160 ft DH3, 45, 45 Depth 100 ft DH4, 90, 45 Depth 100 ft DH5, 135, 45 Depth 100 ft DH6, 315, 45 Depth 80 ft Kl, Lake Wohlford Granodiorite
Ks, San Marcos Gabbro
Ksa, San Marcos Anorthositic Gabbro Kp, Pegmatite
Unimproved roads
Drill hole locations were recorded using northing and easting coordinates (transverse mercator, North American Datum of 1927). Geologic core logging was performed at the drilling site followed by moving the core to the San Pasqual Tribe’s Community Development office for photographing (Figure 3.2). Samples for aggregate properties testing were prepared using the entire core at 18 to 30 foot (5.5 to 9 meter) intervals and were transported to San Diego Testing Engineers.
3.4.1 Geologic Core Logging
Geologic logs included rock descriptions, rock quality designation (RQD; section 3.4.2), percent recovery, estimated weathering, and estimated strength. Each rock unit was described as it was encountered including the following information:
ROCK TYPE Color, grain size estimates, grain descriptions, rock type, estimated strength, estimated weathering, estimated moisture content, bedding character, any notes or comments.
Included features such as pegmatites or quartz veins were noted on the log as they were encountered.
3.4.2 Rock Quality Designation
RQD is the percentage of sound core sections greater than four inches long compared to the total length of the core run. RQD is calculated by measuring the length of the core sections greater than four inches and dividing this total by the total length of the core run (after Deere, 1968, in Brady and Brown, 1999). As the RQD values represent the percentage of intact rock, higher values indicate the least weathered and fractured rock.
3.4.3 Core Recovery
The percentage of core recovery is calculated using the driller’s measurement of the single core run drilled compared with the length of the core recovered from the drill rig. This is influenced by fracturing in the rock and the handling of the core by the driller. Core recovery was used to measure the amount of core lost during drilling.
3.4.4 Weathering Scale
The degree of weathering of the material was classified through the system in Table 3.3. Weathering in the field was estimated from examination of the core and from tapping the core with the rock hammer.
3.4.5 Strength Scale
Strength was estimated following the classification system shown in Table 3.4. The strength estimate is based on the resistance of the core sample to breaking or crumbling. This classification was made during logging through scratching the core by hand, with a knife, and by tapping the core with a rock hammer.
Table 3.3:
Relative scale of weathering1.
Log Sheet Symbol
Grade Diagnostic Features
FR Fresh No visible signs of decomposition or discoloration. Rings when struck by hammer.
SW Slightly
weathered
Slight discoloration inwards from open fractures, otherwise similar to FR.
MW Moderately
weathered
Discoloration throughout. Weaker minerals such as feldspar decomposed. Strength somewhat less than fresh rock but cores cannot be broken by hand or scraped by knife. Texture preserved.
HW Highly
weathered
Most minerals somewhat decomposed. Specimens can be broken by hand with effort or shaved with a knife. Core stones present in rock mass. Texture becoming indistinct but fabric preserved.
XW Extremely
weathered
Minerals decomposed to soil but fabric and structure preserved (saprolite). Specimens easily crumbled or penetrated.
Clays Completely weathered residual soil
Advanced state of decomposition resulting in plastic soils (colluvium). Rock fabric and structure completely destroyed. Large volume change.
Table 3.4:
Relative scale of strength1.
Log Sheet Symbol
Class Strength Field Test Approximate
Range of Uniaxial Compressive Strength kg/cm2 VS I Very Strong Many blows with geologic hammer
required to break intact specimen
> 2000 S II Strong Hand held specimen breaks with
hammer end of pick under more than one blow.
2000 – 1000
MS III Moderately Strong
Cannot be scraped or peeled with knife, hand held specimen can be broken with single moderate blow with pick.
1000 – 500
W IV Weak Can just be scraped or peeled with knife. Indentations 1mm to 3mm show in specimen with moderate blow with pick.
500 – 125
VW V Very Weak Material crumbles under moderate blow with sharp end of pick and can be peeled with knife but is too hard to hand trim for triaxial test specimen
125 – 12
1. After NAVFAC, 1982
3.5 Sample Testing Program
Each sample was collected according to the American Society for Testing and Materials (ASTM) standard D75-97 (ASTM D75, 1997). The samples were either tested at the Colorado School of Mines or the Testing Engineers of San Diego laboratory. The testing performed depended on the phase of work and the goal of the testing. Aggregate
tests followed California Test (CT) procedures where possible; tests that could not be run under CT procedures followed ASTM procedures.
Reconnaissance samples were subjected to crushing at Hazen Research Inc. followed by Los Angeles abrasion testing (ASTM C131, 1996). The Los Angeles abrasion test was chosen to provide an initial indication of material quality.
Sieve analysis (ASTM C136, 1996), sand equivalent value (Caltrans
Transportation Laboratory CT 217, 1999), durability index (Caltrans Transportation Laboratory CT 229, 2000), specific gravity (ASTM C127, 2001 and ASTM C128, 2001), stabilometer value or resistance value (R-Value) (Caltrans Transportation Laboratory CT 301, 2000), sodium sulfate soundness (ASTM C88, 1990), and Los Angeles abrasion tests were performed on samples obtained from the drilling investigation in district C. Not every sample was subjected to every test.
3.5.1 Sand Equivalent
The sand equivalent test (Caltrans Transportation Laboratory CT 217, 1999) determines the relative amounts of silt and clay that have adhered to larger rock particles. This is achieved through adding a measured volume of soil to a volume of flocculating solution. The mixture is then agitated to force the clay coatings into suspension. The height of the sand column present divided by the measured height of the fines in
suspension provides the numerical value for the test. Figure 3.3 is a photograph of the test illustrating the values that are measured. Higher numbers indicate less clay is in
Measured Clay Height
Sand Height
Actual
Clay Height
Measured Clay Height
Sand Height
Actual
Clay Height
Figure 3.3 Sand equivalent test measurements.
This test is part of Caltrans specifications for fine aggregate. Table 3.5 lists the operating range specifications for Caltrans and FHWA regarding the sand equivalent value for multiple construction material applications.
Table 3.5:
Sand equivalent specifications (minimum values).
Construction Material Caltrans1 FHWA2
Minimum sand equivalent value
Portland Cement Concrete 75 75
Asphalt Concrete 50 45
Aggregate Base 25
Class 1 Subbase 21
Class 2 Subbase 21
Class 3 Subbase 21
1. California Department of Transportation, 2002. 2. Federal Highway Administration, 1996.
3.5.2 Los Angeles Abrasion
The Los Angeles abrasion (Rattler) test (ASTM C131, 1996) is the most widely specified test for measuring the resistance of an aggregate to degradation through
abrasion and impact. The test consists of subjecting a measured sample of four specified grain sizes to 500 revolutions in the Los Angeles abrasion testing device (Figure 3.4). The material is then agitated on the #12 sieve with the material retained being weighed. This provides a percentage of the material lost through the abrasion process which can be used to predict aggregate performance under abrasion and impact stresses. For this test, lower percentage losses indicate better material.
Figure 3.4 Los Angeles abrasion test equipment.
Percentage loss values were also determined at 100 revolutions for comparison to Caltrans specifications and to allow calculation of the coefficient of uniform hardness. The coefficient of uniform hardness is the ratio of the percentage loss of the material at 100 revolutions to the percentage loss of the material at 500 revolutions. This provides a measure of the homogeneity of the aggregate material. The optimum coefficient of uniform hardness value is 0.20. Higher coefficient numbers indicate that the aggregate sample is degrading early in the test. Los Angeles abrasion test values are calculated as follows:
LA100 = ((M0 – M100)/(M0)) * 100
LA500 = ((M0 – M500)/(M0)) * 100
Cunhd = LA100 / LA500
LA100 = LA abrasion # after 100 revolutions
LA500 = LA abrasion # after 500 revolutions
Cunhd = Coefficient of uniform hardness
M0 = Total original mass of sample
M100 = Mass of the sample retained on the #12 sieve after 100 revolutions
M500 = Mass of the sample retained on the #12 sieve after 500 revolutions
This test is part of Caltrans specifications for a variety of construction material applications. FHWA specifications are also listed for comparison and reference. Table 3.6 lists specifications for the Los Angeles abrasion test.
Table 3.6:
Los Angeles abrasion test specifications (maximum values).
Construction Material Caltrans1 FHWA2 Los Angeles abrasion at 100 revolutions (%) Los Angeles abrasion at 500 revolutions (%) Los Angeles abrasion at 500 revolutions (%) Portland Cement Concrete 45 40 Asphalt Concrete 10 40 40
Base, Subbase, and Surface Course
50
1. California Department of Transportation, 2002. 2. Federal Highway Administration, 1996.
3.5.3 Sieve Analysis
Sieve analysis (ASTM C136, 1996) defines the grain size distribution in a deposit, which is part of material specifications. The test consists of loading a material sample onto a stack of sieves with decreasing openings, ie the top screen has the largest opening. The sample is shaken such that individual particles are exposed in several different orientations to the screen openings. The sieve analysis results are the weight of material retained on each screen, generally reported as a percentage of the total weight of the sample. Screens used for sieve analyses were based on Caltrans specifications and are listed in Table 3.7.
3.5.4 Durability Index
The durability index test (Caltrans Transportation Laboratory CT 229, 2000) measures the resistance of material to degradation when exposed to water and abrasion. The test is similar to the sand equivalent test in that the test material is placed in a sand equivalent cylinder with a measured amount of water. The material is then agitated in the cylinder for a period of ten minutes and a flocculating solution of calcium chloride is added to the cylinder. After a period of twenty minutes the clay height and sand height are determined as in the sand equivalent test. This provides a measure of the amount of fines produced during the agitation. Higher durability index values indicate better aggregate material.
Table 3.7:
Sieve sizes used for grain size distribution analysis.
Sieve Size (mm) Sieve Size (inches) Sieve Size (American
Number) 37.5 1 ½ 25 1 19 ¾ 12.5 ½ 9.5 3/8 4.75 ¼ # 4 2.36 1/8 # 8 1.18 1/16 # 16 0.6 1/30 # 30 0.3 1/50 #50 0.15 1/100 #100 0.075 1/200 # 200
The durability index test can be run with a fine gradation sample or a coarse gradation sample. When both gradations are tested, the lower result is considered the durability index value with respect to adherence to specifications. The durability index test is part of Caltrans specifications for fine aggregate. Table 3.8 lists Caltrans and FHWA specifications for several construction materials.
Table 3.8:
Durability index specifications.
Construction Material Caltrans1 FHWA2
Minimum durability index value Portland Cement Concrete 60
Asphalt Concrete 50 35
Aggregate Base 35 35
Class 1 Subbase 35
Class 2 Subbase 35
Class 3 Subbase 35
1. California Department of Transportation, 2002. 2. Federal Highway Administration, 1996.
3.5.5 Resistance Value
The R-Value index test (Caltrans Transportation Laboratory CT 301, 2000) measures the deformation of a specimen under load. Higher values indicate a stiffer, higher density material. For instance, water would have an R-value of zero while a solid rock cube would have an R-value of 100.
Measurement of the value is achieved through molding a test sample into an R-value container. This sample is subjected to vertical and horizontal loads. After the loads have been applied, the sample is measured to determine the amount of deformation that has occurred. The amount of deformation and the moisture content is graphed to
determine the R-value. Table 3.9 lists specifications for the R-value test from Caltrans. The R-value test is not referenced by the FHWA.
Table 3.9:
R-value specifications (minimum values).
Construction Material Caltrans1
Aggregate Base 78
Class 1 Subbase 60
Class 2 Subbase 50
Class 3 Subbase 40
1. California Department of Transportation, 2002.
3.5.6 Sulfate Soundness
The sulfate soundness test (ASTM C88, 1990) is an index of the resistance of the rock to breakdown from freeze-thaw. Simulation of this stress is accomplished through the repeated immersion of the sample in saturated solutions of sodium or magnesium sulfate followed by oven drying to dehydrate the salt precipitated in pore spaces. The internal expansive force, derived from the rehydration of the salt upon re-immersion, creates the simulation of the expansion of water on freezing (ASTM C88, 1990). At the end of five immersion cycles, the sample is sieved on a screen with an opening of one half the size of the original maximum grain size of the sample. Sample material that is retained on this half size sieve is weighed to determine the percentage loss. For this test, low percentage losses indicate the best material.
This test is part of Caltrans specifications for materials used in Portland cement concrete. The Caltrans specification for the soundness test requires a maximum of 10% loss recorded by the test (California Department of Transportation, 2002).
3.5.7 Specific Gravity
Specific gravity (ASTM C127, 2001 and ASTM C128, 2001) provides a value of the density for coarse or fine aggregate normalized against the density of water. For coarse aggregate the sample is weighed dry and then weighed wet using a large basket assembly. The dry weight of the sample is divided by the weight of the sample and the water. For fine aggregate a known volume of water is weighed in a volumetric
(pycnometer or Le Chatelier) flask. Then the sample of aggregate is added to the flask with the water and weighed. The aggregate is then dried and weighed again. The dry weight of the sample is divided by the weight of the flask filled with water minus the weight of the flask with water and aggregate.
The specific gravity value can be used to estimate the mass of a deposit from volume measurements or to detect deleterious materials in the aggregate such as iron bearing minerals which typically increase the specific gravity. Specific gravity values that are generally acceptable for aggregate use range between 2.68 and 2.80 (Langer and Knepper, 1995).
CHAPTER 4.0
RESULTS
4.1 Literature Review and Database Construction
Glynn (2000) provided geologic data and subsurface information for District C of the SPBMIR. The study included geologic logs from 11 boreholes, grain size distribution results, Atterberg limits results, and R-Value results from surface and borehole samples (Appendix A). The boreholes were all vertical and ranged from 30 to 80 feet (9 to 24 meters) deep (Plate B).
Borehole logs (Appendix A) describe San Marcos Gabbro and Lake Wohlford Granodiorite in the subsurface. In general, the logs describe weathered gabbro with corestones overlying moderately weathered, medium hard to soft gabbro overlying slightly weathered hard gabbro. From the rock description, BH4 additionally encountered San Marcos Anorthositic Gabbro. RQD values from the logs range from 10 to 100 with average values between 65 and 100 for all the boreholes suggesting high quality rock. Grain size distributions were conducted on samples of decomposed gabbro collected between 0 to 3 feet (0 to 1 meter) BGS from BH3, BH4, BH8, and from an unknown roadcut. The material chosen for the samples is described as decomposed gabbro. The maximum grain size was ½ inch for BH3, 3/8 inch for BH8 and the roadcut, and ¼ inch for BH4. The percentage of fines from the samples ranges from 9 to 35%.
Atterberg limits were conducted for samples from BH4 and BH8 of the Glynn (2000) study. The liquid limit for BH4 was 33, the plasticity index was 18 and it was classified as clayey sand (SC). The liquid limit for BH8 was 36, the plasticity index was 20 and it was classified as clayey sand (SC). The unknown roadcut sample of
decomposed gabbro, grey silty sand (SM), was subjected to an R-Value test which equaled 74.
Following the database construction, the information for the SPBMIR was reviewed. In particular, the aerial photographs and topographic maps were examined to determine access to areas across the SPBMIR for the reconnaissance geologic phase of the study. Review of the aerial photographs and information from the Tribe indicated that several key structures including the Valley View Casino and the San Pasqual Tribal Headquarters along with a high density of housing existed in District B of the SPBMIR. Due to this higher development density it was determined that District B would not be a target of any further investigation.
4.2 Reconnaissance Investigation
Field mapping trips occurred from May 22 to May 24, 2003 and August 6 to August 14, 2004. Exposed contacts for geologic units were mapped onto base maps produced from the GIS database for districts A, A-2, C, and C-2. Buried contacts were mapped through observing float and rock outcrops. Outcrop geology was described in the field and hand samples and aggregate properties testing samples were collected.
4.2.1 Lithologic and Petrographic Examination and Geologic Descriptions
Twelve thin sections were produced from hand samples collected during the field mapping trips. Two thin sections were from the pegmatite units, three from the Lake Wohlford Granodiorite, two from the Bonsall Tonalite, three from the San Marcos Gabbro, one from the San Marcos anorthositic gabbro and one from the Bedford Canyon Formation quartzite.
4.2.1.1 Pegmatites (Kp, Cretaceous)
The pegmatites are white to light gray with minor pink or tan tones and weather to a light orange or a darker pink (Figure 4.1). Crystal sizes range from two millimeters up to 250 millimeters. Smaller grains can be anhedral or euhedral while larger grains are euhedral. Smaller grained pegmatites can be very friable.
Thin sections of the pegmatites are equigranular. The quartz, potassium feldspar, and plagioclase are anhedral while the muscovite is euhedral. All the crystals display slight weathering along their edges and several display elongation deformation. Figures 4.2 and 4.3 are photomicrographs of the thin sections.
Minerals found in the thin sections of the pegmatites varied slightly by district. The pegmatite sample from district A was composed entirely of quartz, potassium feldspar, and plagioclase and the sample from district C contained the same minerals as well as muscovite. Mineral compositions from the thin sections are in Table 4.1.
4.2.1.2 Lake Wohlford Granodiorite (Kl, Cretaceous)
Colors of the Lake Wohlford Granodiorite range from very light tan to orange reddish brown speckled with pink (Figure 4.4). The color varies based on the degree of weathering and the amount of biotite present in the sample. Samples can be very friable. Grain size in the hand samples ranges from one to three millimeters in size with
subhedral to anhedral quartz, plagioclase, potassium feldspar, and magnetite and euhedral biotite. Other minerals listed in the literature for the Lake Wohlford Granodiorite include
Figure 4.1 In-situ pegmatite from District C.
Figure 4.2 Elongated quartz crystals under cross polarized light in thin section SP-2. Field of view (FOV) is 1.55 millimeters.
Figure 4.3 Muscovite in thin section SP-1 under cross polarized light from District C. FOV is 1.55 millimeters.
Table 4.1:
Mineral composition from thin sections SP-1 and SP-2
Mineral Thin Section SP-1 (District C) Thin Section SP-2 (District A)
Quartz 40% 80% Potassium feldspar 40% 15% Plagioclase 15% 5% Muscovite 5% 0%
muscovite, hornblende, apatite, sphene, and zircon (Jahns and Wright, 1951). The IUGS classification for the Lake Wohlford Granodiorite in the study area is biotite granodiorite.
In outcrop in District C-2, the Lake Wohlford Granodiorite displays one consistent joint set. This is a steeply dipping joint set striking approximately east-west and dipping approximately 70 to 90 degrees south (Figure 4.4). The strike of the joint set
Muscovite
Quartz
