Characterization of Northern California 

Petroleum by stable carbon isotopes 

[paper edition] 

by Paul G. Lillis1

, Leslie B. Magoon, Richard G. Stanley, Robert J. 

McLaughlin, and Augusta Warden 

Open-File Report 99-164 

2001 

This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey 

editorial standards or with the North American Stratigraphic Code. Any use of trade, firm, or product 

names is for descriptive purposes only and does not imply endorsement by the U.S. Government. 

U.S. DEPARTMENT OF THE INTERIOR 

U.S. GEOLOGICAL SURVEY 

1

Denver, Colorado 
2

Introduction 

The purpose of this study is to characterize natural occurrences of petroleum at the 

surface and in the subsurface within northern California in order to define and map petroleum 

systems for U.S. Geological Survey energy resource assessments. Furthermore, the chemical 

characterization and mapping of natural petroleum occurrences could also be used to 

discriminate natural occurrences from accidental oil spills during the activities of extraction or 

transportation of petroleum. Samples include petroleum from exploratory well tests, producing 

fields, natural seeps, and oil-stained rocks, and condensates from gas wells. Most of the sample 

localities are in northern California but a few samples from central and southern California are 

included for comparison (table 1). Even though other analyses were performed, only stable 

carbon isotope (δ13C) data are presented here for brevity and because δ13C values are one of the 

most discriminating characteristics of California petroleum. 

 

Magoon and others (1995) identified four hydrocarbon types in northern California based 

on stable carbon isotopic compositions of 16 oil and 6 condensate samples (figure 1). Stanley

and others (1996) presented additional data and focused on the oil types found in the San 

Francisco Bay area of northern California. Lillis and Stanley (1999) identified three oil types 

(two Miocene and one Eocene) in the La Honda basin (northern California) and presented oilsource rock correlations for each oil type. This report redefines and subdivides the petroleum 

types based on the isotope data from these studies as well as from new data. 

Methods 

For oil-stained rocks, the oil was extracted from the rock sample by soaking the sample in 

chloroform for about one hour at room temperature. Filtered extracts were vacuum evaporated to 

about 3 milliliters (ml) using a rotary evaporator with moderate vacuum and water bath 

temperature of about 35° C, and transferred to a volumetric flask for a gravimetric determination 

of concentration. An aliquot of known concentration was placed in a vial and the volume was 

reduced to approximately 1 ml in a stream of nitrogen gas at room temperature. About 2 ml of 

iso-octane was added and mixed with a vortex mixer on low speed, and gently evaporated in a 

stream of nitrogen gas to about 1 ml. The iso-octane addition and evaporation step was repeated 

at least three times until the chloroform was completely displaced by iso-octane precipitating the 

asphaltene fraction of the oil out of solution. The asphaltenes were removed by filtration and the 

remaining solution (maltene fraction) was gently evaporated in a stream of nitrogen to about 1 

ml in preparation for column chromatography. 

For petroleum samples, about 50 milligrams of oil sample was mixed with about 2 

milliliters (ml) iso-octane (1:40 weight/volume ratio) with a vortex mixer on low speed. The 

asphaltene fraction of the oil precipitated out of solution and was removed by filtration. The 

maltene fraction (prepared from both oil-stained rocks and from petroleum samples) was 

separated into saturated hydrocarbon, aromatic hydrocarbon, and resin fractions by column 

chromatography using alumina/silica columns and elution solvents of increasing polarity (isooctane, benzene, and benzene-methanol). Elution solvents and light hydrocarbons (less than C15) 

were removed from each fraction by evaporation using a nitrogen gas stream under a fume hood 

or a rotary vacuum evaporator. 
3

Stable carbon isotope ratios were determined for the C15+ saturated and aromatic 

hydrocarbon fractions, and in a few cases, the entire oil sample. Two methods were utilized that 

are believed to have comparable results. Prior to 1997 all isotope measurements were determined 

by placing an aliquot of each sample in a quartz tube with cupric oxide and a silver strip. The 

tubes were sealed under a vacuum and combusted at 840°C for 4 hours. The evolved CO2 was 

collected in a liquid nitrogen trap, and further purification and dehydration of the gas was 

accomplished by cryogenic distillation under vacuum. Carbon isotope ratios of the CO2 were 

measured on a Finnigan MAT 251 dual-inlet isotope ratio mass spectrometer. During 1997 a 

change in instrumentation occurred and during the transition both old and new methods were 

used. After 1997 all samples were analyzed with a Carlo Erba elemental analyzer (EA) 

interfaced with a Micromass Optima continuous-flow isotope ratio mass spectrometer (IRMS). 

Sample aliquots were heated to approximately 1800°C in the EA quartz combustion tube filled 

with oxygen. The evolved CO2 passed through chromium oxide (to complete oxidation), copper 

granules (reducing agent), and anhydrone (to remove water) before being swept into the IRMS 

with a helium carrier gas. The results are expressed in the delta (δ) notation that represents the 

deviation of the 13C/12C ratio in parts per thousand (per mil, or ‰) relative to the Peedee 

belemnite (PDB) standard. 

Results and Discussion 

Results of the stable carbon isotopic analyses (δ13C) are listed on table 1 and shown on 

figure 2 along with a line proposed by Sofer (1984) that separates waxy oils from non-waxy oils. 

Waxy oils are usually derived from terrigenous organic matter, whereas non-waxy oils are 

usually derived from marine organic matter. Nearly all of the samples plot on the marine side of 

the Sofer line (figure 2). Polygonal boundaries that are roughly parallel to the Sofer line trend are 

placed around data groups (table 2). Unclassified samples are individually labeled on figure 2. 

Classification of condensate samples into oil types using the δ13C values of the C15+ hydrocarbon 

fractions is problematic for two reasons. First, condensates are predominately composed of 

volatile hydrocarbons and the C15+ fraction of the saturated and aromatic hydrocarbons 

constitutes only a small weight percentage of the total sample. Thus, the C15+ stable carbon 

isotope values of condensates are not as representative as are the values for normal crude oil. 

Second, the saturate/aromatic hydrocarbon ratio is usually so high (greater than 10) that the C15+ 

aromatic fraction weight is too small to measure the δ13C value. In many cases, column 

chromatography was not performed and the isotope measurement was made on the C15 + whole 

oil. In addition to these methodology problems, there is some question as to whether condensates 

should be compared with crude oils; that is, condensates are not crude oils but rather are the 

minor liquid fraction that condenses out of gas during natural gas production. For these reasons, 

the condensates are classified as separate groups. 

Cretaceous (K) Oil Group 

K1 Subgroup

The K1 samples were collected from the Wilbur Springs area east of Clear Lake and 

include several oil seeps and an oil sample from an exploratory well. Although the source is 

unknown, K1 oils are speculated to be derived from Cretaceous source rocks based on the age of 

the rocks in which the oil is found (Early Cretaceous). Furthermore, Peabody (1990) found that 

petroleum from the Wilbur Springs quicksilver district has a chemical composition compatible 

with the Tithonian to Valanginian Stony Creek Formation as their primary source. Magoon and 

others (1995, 1996) considered oil samples from the Arbuckle and Bunker gas fields (Oils 26-28, 

table 1) to be part of this group, but are here classified with K4 oils discussed below. The 
4

McLaughlin Mine (Oil 103) and Rathbun (Oil 105) seeps are isotopically heavier than the other 

K1 seeps, possibly due to mixing of Miocene with Cretaceous sources. 

K2 Subgroup

Many of the mercury deposits of the California Coast Ranges have small quantities of oil, 

solid bitumen, and hydrocarbon minerals that are genetically associated with the mercury ore 

(Bailey, 1959; Peabody, 1990, 1993; Peabody and Einaudi, 1992). The K2 samples are oils 

genetically associated with mercury deposits and have an isotopic composition similar to the 

other Cretaceous oils. However, three samples associated with mercury ore are isotopically 

distinct from the K2 subgroup: (1) the oil in vugs of the mercury ore from the Mirabel Mine (Oil 

107), (2) the curtisite sample (a hydrocarbon mineral) from the Mirabel Mine (Oil 108), and (3) 

an oil-coated silica gel in mercury-bearing silica-carbonate rock from near the Helen mine (Oil 

109). 

K3 and K4 Subgroups

The K3 and K4 samples are liquid hydrocarbons produced from gas fields along the west 

side of the Sacramento basin. The K3 samples are clear to straw-yellow liquids with insufficient 

C15+ aromatic hydrocarbons to measure δ13C values, whereas the K4 samples are yellow, red, 

and brown liquids and have measurable δ13C aromatic hydrocarbon values. All of K3 and some 

of K4 samples are assumed to be condensates based on their light color, high saturated/aromatic 

hydrocarbon ratio (greater than 10) and their origin from gas fields. The K4 samples from 

Arbuckle, Bunker, and Winters gas fields have a darker color and lower saturated/aromatic 

hydrocarbon ratio (less than 8) and are reported to be oils; the Winters gas field has had minor oil 

production (California Division of Oil and Gas, 1983). The K3 and K4 samples are speculated to 

be derived from Cretaceous source rocks based on their intimate association with natural gas 

accumulations that, in turn, are believed to be derived from Cretaceous source rocks (Magoon 

and others, 1994). Although K4 and K1 samples have similar isotopic compositions, they are 

considered separate groups because K4 samples have an association with gas production. 

Sherman Island (Oil 106) and Concord (Oil 101) gas field condensate samples are located in the 

same area (west side of Sacramento basin) as the K3 and K4 samples, but are isotopically 

distinct possibly due to mixing of Eocene and Cretaceous sources. 

Eocene Oil Group 

The Eocene oil group includes crude oil samples from three northern California oil fields: 

Brentwood, Livermore, and Oil Creek. Several oils analyzed from central and southern 

California fall into the Eocene group, including samples from Coalinga, North Antelope Hills, 

and Antelope Hills oil fields. These oils are believed to be derived from Eocene source rocks 

based on similar isotopic composition with other proposed Eocene oils in California (Sofer, 

1984; Kornacki and McNeil, 1996) and based on oil-source rock correlation studies (Peters and 

others, 1994; Lillis and Stanley, 1999). The produced oil from Cymric field (Oil 102) is probably 

a mixture of Eocene and Miocene oils based on correlations of other Cymric oils to either 

Eocene or Miocene sources (Peters and others, 1994). 

Miocene Oil Group 

M1 Subgroup

The M1 oil group consists of four crude oils from the Half Moon Bay field, San Mateo 

County. Lillis and Stanley (1999) show that the source of these oils is the lower Miocene 

Lambert Shale, and that these oils are isotopically heavier than oils derived from middle and 

upper Miocene source rocks. Similarly, oils from lower Miocene source rocks in central 
5

California are isotopically heavier than the middle and upper Miocene Monterey oils (Kornacki, 

1988; Lillis, 1988; Lillis, 1994; Peters and others, 1994; Kornacki, 1996). 

M2 Subgroup

The M2 oil group includes oil seeps and stains from Marin, Mendocino, Santa Cruz and 

San Mateo Counties and most of the northern California oil field samples including Petrolia, 

Petaluma, Pinole Point, La Honda, South La Honda and Sargent fields (table 1). Nearly all oils 

analyzed from central and southern California oil fields fall into the M2 group, including South 

Belridge, Edison, Hollister, King City, San Ardo, Kern Front, and portions of Antelope Hills. 

Magoon and others (1995) defined the Miocene oil group boundaries with saturated 

hydrocarbons being -22.9 ± 0.6‰ and the aromatic hydrocarbons being -22.1 ± 0.5‰ (figure 1). 

We redefine the boundaries as shown on figure 2 and listed in table 2. These oils are likely 

derived from middle and upper Miocene marine source rocks (mostly Monterey Formation but 

also including some other units) based on similar isotopic composition with other Miocene oils 

in California (Magoon and Isaacs, 1983; Sofer, 1984; Crain and others, 1985; Curiale and others, 

1985; Orr, 1986; Zumberge, 1987; Kornacki, 1988; Lillis, 1988; Lundell and Gordon, 1988; 

Sofer, 1988; Jeffrey, and others, 1991; Lillis, 1994; Peters and others, 1994; Kornacki, 1996). 

M3 Subgroup

Two condensate samples from the Tompkins Hill gas field are classified as a separate 

subgroup (M3) because of their distinct isotopic composition, although we consider them to be 

genetically related to the Petrolia oils (subgroup M2). We speculate that the Tompkins Hill 

condensate δ13C saturated hydrocarbon values are lower (isotopically lighter) because the source 

rock has higher amounts of Miocene vascular plants and/or pre-Miocene organic matter. 

However, the δ13C aromatic hydrocarbon values may be lower due to low sample weights. The 

composition of the oil from Table Bluff gas field (Oil 110) is suspiciously different from the 

Tompkins Hill condensates although both fields share the same stratigraphy and producing 

formation and are in close proximity (less than 5 miles). The Table Bluff sample was donated 

from the Chevron oil collection and we speculate that the sample may be mislabeled. 

M4 Subgroup

 The M4 samples are mudstones and sandstones with a kerosene odor (the so-called "stink 

muds") exposed in the sea cliffs in the False Cape and Bear River areas of Humboldt County. 

Gas chromatography and δ13C hydrocarbon data suggest that these oils are genetically related to 

the Tompkins Hill (M3) and Petrolia oils (M2). However, most of these samples plot farther 

from the Sofer line than the other Miocene oils. This shift is possibly due to low aromatic 

hydrocarbon sample weights that may yield lower the δ13C aromatic hydrocarbon values. 

Because these “stink muds” are an unusual sample type and have slightly different isotopic 

characteristics, they are excluded from the Miocene boundary box. Sample 104 is 

compositionally distinct from all other oil-stained rocks collected in Humboldt County (M4 oils), 

and may be derived from sources older than Miocene. 
6

Conclusions 

Naturally occurring petroleum in northern California can be classified into Cretaceous, 

Eocene, or Miocene oil groups based on δ13C hydrocarbon composition. Cretaceous subgroups 

include oil seeps from the Wilbur Springs area (K1), oil associated with mercury deposits (K2), 

and condensates and oils associated with natural gas production (K3 and K4). Miocene 

subgroups include lower Miocene oils (M1), middle and upper Miocene oils (M2), Tompkins 

Hill condensate (M3), and Humboldt County oil seeps (M4). 

Acknowledgments 

Many of the oil samples used for this paper originated from Chevron Oil Company, Shell Oil 

Company, and California Division of Oil, Gas and Geothermal Resources; we thank these 

organizations for their cooperation. We are especially indebted to the following individuals from 

these organizations and many others that provided oil samples: Patricia Abel, Richard W. Boyd, 

Jack Castaño, M.P. Dempsey, Jim Elison, Dave Haglund, Scott Hector, Dean Enderlin, Nat 

MacKevett, Kenneth Peters, Gary Reed, Sarge Reynolds and Larry Tedesco. We would also like 

to thank IHS Energy for permission to publish latitude/longitude data that they provided. Finally 

we thank Charles Threlkeld and Michael Lewan for their critical reviews of the manuscript. 
7

References 

Bailey, E.H., 1959, Froth veins, formed by immiscible hydrothermal fluids, in mercury deposits, 

California: Geological Society of America Bulletin, v. 70, p.661-664. 

California Division of Oil and Gas, 1983, California oil and gas fields – Northern California, 

TR10, Winters Gas Field data sheet. 

Crain, W.E., Mero, W.E. and Patterson, D., 1985, Geology of the Point Arguello discovery: 

American Association of Petroleum Geologists Bulletin, v. 69, p.537-545. 

Curiale, J.A., Cameron, D., and Davis, D.V., 1985, Biological marker distribution and 

significance in oils and rocks of the Monterey Formation, California: Geochimica 

Cosmochimica Acta, v. 49, p. 271-288. 

Jeffrey, A.W.A., Alimi, H.M. and Jenden, P.D., 1991, Geochemistry of Los Angeles 

Basin oil and gas systems, in Biddle, K.T., ed., Active Margin Basins: American 

Association of Petroleum Geologists Memoir 52, p.197-219. 

Kornacki, A.S., 1988, Provenance of oil in southern Cuyama basin, California [abs]: 

American Association of Petroleum Geologists Bulletin, v.72 no.2 p.207. 

Kornacki, A.S., 1996, Petroleum geology and geochemistry of Miocene source rocks and 

heavy petroleum samples from Huasna basin, California, in Schumacher, D. and 

Abrams, M.A., eds., Hydrocarbon migration and its near-surface expression: 

American Association of Petroleum Geologists Memoir 66, p. 413-430. 

Kornacki, A.S., and McNeil, R.I., 1996, Chemistry and origin of Miocene and Eocene oils and 

tars in the onshore and offshore Santa Cruz Basins, California [abs]: Annual Meeting 

Abstracts - American Association of Petroleum Geologists and Society of Economic 

Paleontologists and Mineralogists, v.5, p.77. 

Lillis, P.G., 1988, Correlation and characterization of oils using biological markers, 

Cuyama basin, California, in Bazeley, W. J. M., ed., 1988, Tertiary tectonics and 

sedimentation in the Cuyama basin, San Luis Obispo, Santa Barbara, and Ventura 

Counties, California: Pacific Section Society of Economic Paleontologists and 

Mineralogists, v. 59, p. 39- 48. 

Lillis, P.G., 1994, Soda Lake-Painted Rock (!) petroleum system in the Cuyama basin, 

California, U.S.A., in Magoon, L.B., and Dow, W.G., eds., The petroleum system--from 

source to trap: American Association of Petroleum Geologists Memoir 60, p. 437-451. 

Lillis, P.G. and Stanley, R.G., 1999, Petroleum systems of the La Honda Basin, California: 

American Association of Petroleum Geologists Bulletin, v. 83, p. 694. 

Lundell, L. and Gordon, S., 1988, Origin of Cuyama oils, in Bazeley, W.J.M., ed., 1988, 

Tertiary tectonics and sedimentation in the Cuyama basin, San Luis Obispo, Santa 

Barbara, and Ventura Counties, California: Pacific Section Society of Economic 

Paleontologists and Mineralogists, v. 59, p. 29- 37. 
8

Magoon, L.B., Lillis, P.G., Warden, A., Stanley, R.G., MacKevett, N.H., and Castaño, J., 1995, 

Carbon isotopic composition identify four hydrocarbon types in northern California [abs]: 

American Association of Petroleum Geologists Bulletin, v. 79, p. 592. 

Magoon, L.B., 1988, The petroleum system--A classification scheme for research, 

exploration, and resource assessment, in Magoon, L.B., ed., Petroleum systems of 

the United States: U.S. Geological Survey Bulletin 1870, p. 2-15. 

Magoon, L.B., Jr., and Isaacs, C.M. (1983), Chemical characteristics of some crude oils from the 

Santa Maria basin, California, in Isaacs, C.M., and Garrison, R.E., eds., Petroleum 

generation and occurrence in the Miocene Monterey Formation, California: Los Angeles, 

Pacific Section, Society of Economic Paleontologists and Mineralogists, p. 201-211. 

Magoon, L.B., Lillis, P.G., and Stanley, R.G., 1996, Carbon isotopes indicate a common origin 

for oils from mercury and gold deposits and Cretaceous reservoir rocks in northern 

California, California, USA [abs]: Memorias del V Congreso Latinoamericano de 

Geoquimica Organica, Cancun, Mexico, 1996, p. 82. 

 

Orr, W.L., 1986, Kerogen/asphaltene/sulfur relationships in sulfur-rich Monterey oils: Organic 

Geochemistry, v.10, p.499-516. 

Peabody, C.E., 1990, Association of petroleum and cinnabar in mercury deposits of the 

California Coast Ranges, USA: unpublished Ph.D. dissertation, Stanford University, 

Stanford, CA, 256 p. 

Peabody, C.E., 1993, The association of cinnabar and bitumen in mercury deposits of the 

California Coast Ranges, in Parnell, J., Kucha, H., Landais, P., eds, Bitumens in ore 

deposits: Special Publication of the Society for Geology Applied to Mineral Deposits, v. 

9, Springer-Verlag, Berlin, p.178-209 

Peabody, C.E. and Einaudi, M.T., 1992, Origin of petroleum and mercury in the Culver-Baer 

cinnabar deposit, Mayacmas District, California: Economic Geology, v.87, p.1078-1103. 

Peters, K.E., Pytte, M.H., Elam, T.D., and Sundararaman, P., 1994, Identification of petroleum 

systems adjacent to the San Andreas Fault, California, in Magoon, L.B. and Dow, W. 

G., eds., The petroleum system - from source to trap. American Association of 

Petroleum Geologists Memoir 60, p.423-436. 

Stanley, R.G., Jachens, R.C., Kvenvolden, K.A., Hostettler, F.D., Magoon, L.B., and Lillis, P.G., 

1996, Evidence for an oil–bearing sedimentary basin of probable Miocene age beneath 

“Silicon Valley,” California [abs.]: 1996 American Association of Petroleum Geologists 

Annual Convention, San Diego, Official Program, v. 5, p. A133–A134. 

Sofer, Z., 1984, Stable carbon isotope compositions of crude oils: Application to source 

depositional environments and petroleum alteration: American Association of 

Petroleum Geologists Bulletin, v. 68, p.31-49. 

Sofer, Z. 1988, Hydrous pyrolysis of Monterey asphaltenes: Organic Geochemistry, v. 

13, p. 939-945. 
9

Zumberge, J.E., 1987, Terpenoid biomarker distributions in low maturity crude oils: 

Organic Geochemistry, v.11, p.479-496. 
Table 1. Stable carbon isotope composition of crude oils, oil seeps and oil-stained rocks from northern and central California

δ13C δ13C δ13C δ13C

Group Oil# Field (Area) Sample Identification API Number Commentsa Latitudeb Longitudeb SecTwnRngc County Depth or Elevd Producing Formation/Zone Formation Age Satse Arome Oil-Te Oil-We Sample Donator Information Sourcef

K1 1 seep - Culver Ranch Culver Ranch AJ-0997 Heavily biodegraded. 39.05149 -122.40040 22-14N-5W Colusa Lower Cretaceous -25.85 -24.87 Elison & Mackevett LL-5K1 2 seep - Gibson Gusher Gibson Gusher 2 Heavily biodegraded. 39.05231 -122.41023 21-14N-5W Colusa Knoxville Lower Cretaceous -26.31 -24.57 Reynolds, Sarge LL-5, Fm-7, Age-7K1 3 seep - Gibson Gusher Gibson Gusher AJ-0996 Severely biodegraded. 39.05231 -122.41023 21-14N-5W Colusa Knoxville Lower Cretaceous -26.33 -24.58 Elison & Mackevett LL-5, Fm-7, Age-7K1 4 seep - Salt Creek Salt Creek AJ-0999 Heavily biodegraded. 39.10261 -122.33649 31-15N-4W Colusa Upper Cretaceous -26.99 -26.05 Elison & Mackevett LL-5K1 5 seep - Thompson Thompson Seep AJ-0995 Heavily biodegraded. 39.15731 -122.34898 7-15N-4W Colusa -26.47 -25.56 Elison & Mackevett LL-5K1 6 seep - Thompson Thompson Seep 2 Heavily biodegraded. 39.15731 -122.34898 7-15N-4W Colusa -26.62 -25.64 Reynolds, Sarge LL-5K1 7 wildcat well Amalgamated 1 04011002530000 Drill stem test. Aromatics degraded. 39.03119 -122.40415 27-14N-5W Colusa Knoxville Lower Cretaceous -26.96 -25.78 Reynolds, Sarge LL-2K1 8 wildcat well Amalgamated AJ-0998 04011002530000 Drill stem test. Aromatics degraded. 39.03119 -122.40415 27-14N-5W Colusa Knoxville Lower Cretaceous -26.85 -25.74 Elison & Mackevett LL-2K2 9 seep - Abbott Mine Abbott Seep Severely biodegraded. 39.02015 -122.44482 32-14N-5W Lake -26.81 -25.24 Reynolds, Sarge LL-5K2 10 stain - Contact mine Contact mine Oil extract from silica carbonate Hg ore. 38.75917 -122.76333 5-10N-8W Sonoma Elev. 2920 -27.21 -24.22 Lillis & others (USGS) LL-5K2 11 stain - Culver Baer mine Culver Baer mine Oil-filled vugs in silica carbonate Hg ore. 38.78069 -122.81883 24-11N-9W Sonoma -26.70 -24.02 Lillis & others (USGS) LL-5K2 12 stain - Helen mine Helen mine Oil extract in silica carbonate Hg ore. 38.74111 -122.69944 1-10N-8W Lake Elev. 2640 -26.22 nd Lillis & others (USGS) LL-5K2 13 stain - New Almaden Mine New Almaden Mine Oil extract from mecury mine ore. 37.18083 -121.84389 3-9S-1E Santa Clara Franciscan Jurassic-Cretaceous -26.58 -24.34 -24.70 Stanley, Rick (USGS) LL-5K3 14 Dutch Slough (Bethel Island) TransAmer. Development 3 04013001000101 Condensate. 38.00806 -121.64919 21-2N-3E Contra Costa 7520-7580 Martinez/First Massive sand Paleocene nd nd -25.84 -25.15 Reed, Gary (Amer.Expl.Co) LL-2K3 15 Knightsen Cecchini 1-32, RD 2 04013203140000 Condensate. Deep pool S. of Dutch Slough field. 37.97117 -121.67057 32-2N-3E Contra Costa 8767-8873 Mokelumne River/3rd Massive Upper Cretaceous nd nd -26.76 Hector, Scott (Baker Oil & Gas) LL-2K3 16 Lindsey Slough Kroutch 16-1 04095209310000 Condensate. 38.18652 -121.75010 16-4N-2E Solano 5736-5752 Capay/Margaret Hamilton sand Eocene nd nd -26.29 Hector, Scott (Baker Oil & Gas) LL-1K3 17 Maine Prairie Liberty Farms 1 04095201290000 Condensate. 38.29078 -121.71157 11-5N-2E Solano 6163-6165 H&T sand Upper Cretaceous -27.00 nd Chevron LL-2, STR-2K3 18 Maine Prairie WZU 3 (Edward Wineman 2) 04095001560001 Condensate. Moderately degraded. 38.33738 -121.73071 27-6N-2E Solano 4755-4795 Basal Capay Eocene -25.76 nd Chevron LL-2, API-2, STR-2K3 19 Pleasant Creek Shell-Pleasant Creek Unit 5-1 04113000650000 Condensate. Moderately degraded. 38.54603 -122.00356 17-8N-1W Yolo -25.28 nd Chevron LL-2, API-2, STR-2, SmID 2K3 20 Rio Vista (East Midland) RVGU 12 04067000490000 Moderately degraded condensate. Formerly Brannon Island 3. 38.14835 -121.64501 33-4N-3E Sacramento 4450-4495 Mokelumne River/Midland sand Upper Cretaceous nd nd -25.90 -25.38 Amerada Hess LL-2K3 21 Rio Vista (East Midland) RVGU 137 04067000640000 Condensate. Well formerly Kuhn Community 3. 38.12064 -121.66852 8-3N-3E Sacramento 5290-5390 Capay/Margaret Hamilton sand Eocene nd nd -26.27 -26.07 Amerada Hess LL-2K3 22 Rio Vista (West Midland) RVGU 158 (2 Twitchell Fee) 04067001060000 Condensate. Mildly degraded. 38.10930 -121.66224 17-3N-3E Sacramento 5049-5115 Capay/Margaret Hamilton sand Eocene -26.30 nd Amerada Hess LL-2K3 23 Rio Vista (West Midland) Trigueiro 4 04095208620000 Condensate. 38.16744 -121.70349 25-4N-2E Solano 9562-9638 Mokelumne River/Peterson Upper Cretaceous nd nd -26.07 -26.02 Amerada Hess LL-1K3 24 Suisun Bay Suisun Community 7 04095004080000 Condensate. 38.13972 -121.99284 5-3N-1W Solano 4405-4470 Domengine Eocene -26.07 nd Chevron LL-2, API-2, STR-2K3 25 W. Thornton-Walnut Grove Maberto 1 04077002170000 Condensate. 38.22059 -121.44265 4-4N-5E Sacramento -26.66 nd Chevron LL-2, API-2, STR-2, Field-3K4 26 Arbuckle Marsh 1 04011000490000 Heavily biodegraded oil from gas field. 39.00498 -122.08030 4-13N-2W Colusa 6363-6381 Forbes/ F Zone sand Cretaceous -26.94 -25.96 Reynolds, Sarge LL-2K4 27 Bunker O’Keefe 1 04095205810100 Mildly degraded oil from gas field. 38.36390 -121.78449 17-6N-2E Solano 6702-6718 Molelumne River Upper Cretaceous -26.59 -25.13 Boyd, Richard (Capitol Oil) LL-2K4 28 Bunker O’Keefe 1 04095205810000 Mildly degraded oil from gas field. 38.36390 -121.78449 17-6N-2E Solano 6700-6730 Mokelumne River/Lower sand Upper Cretaceous -26.61 -25.29 MacKevett, Nat LL-2K4 29 Kirby Hill Wagenet 2 04095000780000 Condensate. 38.16997 -121.91100 19-4N-1E Solano 5398-5650 Martinez Paleocene -26.57 -25.42 Chevron LL-2, STR-2K4 30 Ryer Island Ryer 3 04095200300000 Condensate. Mildly degraded. 38.07681 -122.01122 30-3N-1W Solano 4300-5000 Nortonville/Domengine Eocene -26.55 -24.53 Haglund, Dave (Shell) LL-2K4 31 Winters McCune 1 04095207160000 Condensate(?) Mildly degraded. 38.49065 -121.88715 32-8N-1E Solano 5576-5585 Winters/McCune? Upper Cretaceous -26.73 -25.14 Haglund, Dave (Shell) LL-2K4 32 Winters McCune 1 04095207160000 Condensate(?) Mildly degraded. 38.49065 -121.88715 32-8N-1E Solano 5600-5600 Winters Upper Cretaceous -26.44 -25.16 Chevron LL-2K4 33 Winters Winters Unit 4-1 (?) 04095004910000 Condensate. Well ID uncertain. Moderately degraded. 38.53123 -121.89718 19-8N-1E Solano 4845-4885 Winters/McCune sand Upper Cretaceous -26.40 -27.12 Chevron SampID-4, LL-2, API-2, STR-2,

E 34 Antelope Hills Hopkins A 56X 04029134410000 Moderately biodegraded. 35.53185 -119.85739 31-27S-20E Kern 2045-2132 Point of Rocks sandstone Upper Eocene -29.20 -28.93 MacKevett, Nat LL-1E 35 Antelope Hills Hopkins A 62X 04029134430000 35.53974 -119.85468 31-27S-20E Kern 2412-2429 Phacoides sand Lower Miocene -29.06 -28.14 MacKevett, Nat LL-1E 36 Antelope Hills, North Fussel Fee 2-14 04030015870000 Moderately biodegraded. 35.57393 -119.90219 14-27S-19E Kern 1560-1636 Phacoides sand Lower Miocene -28.43 -27.75 MacKevett, Nat LL-1E 37 Brentwood (East area) Ginochio 1 04013000750202 37.93694 -121.74488 15-1N-2E Contra Costa 4100-4200 Mokelumne River/3rd Massive Upper Cretaceous -29.40 -27.73 Reed, Gary (Amer.Expl.Co) LL-2E 38 Coalinga Fee 122-13D 04019027420000 Heavily biodegraded. Mixed light saturated hydrocarbons. 36.18475 -120.39792 13-20S-14E Fresno Temblor sand Miocene -27.85 -27.46 Peters, Ken (Chevron) LL-2E 39 Livermore Nissen 3 04001200120000 Mildly biodegraded. 37.69359 -121.68289 7-3S-3E Alameda 1410-1420 Cierbo/Greenville sand Upper Miocene -28.37 -27.20 Reed, Gary (Amer.Expl.Co) LL-2E 40 Livermore Schenone 1 04001200440000 Mildly biodegraded. 37.69519 -121.68423 6-3S-3E Alameda 1500-1510 Cierbo/Greenville sand Upper Miocene -28.34 -27.21 Reed, Gary (Amer.Expl.Co) LL-2E 41 Oil Creek Costa 7-A 04081200200000 37.23927 -122.16484 14-8S-3W San Mateo 1940-2040 Butano/Costa Eocene -28.71 -27.51 Haglund, Dave (Shell) LL-2

M1 42 Half Moon Bay (Verde) Cowell 1 (Wilshire) 04081000080000 Deepest well in field - TD 7982 ft. 37.39722 -122.40471 21-6S-5W San Mateo 1373-2724 Purisima Pliocene -22.80 -21.60 Chevron LL-2, API-2, DE-3, Fm-3, Age-3M1 43 Half Moon Bay (Verde) Cowell Estate 3 (Zia Oil Corp.) 04081200430000 Operator now Midcoast Oil LTD. Partnership. 37.39650 -122.40228 22-6S-5W San Mateo 1732-2242 Purisima Pliocene -22.25 -21.35 Chevron SampID-4, LL-API-2, DE-3, Fm-3, Age-3M1 44 Half Moon Bay (Verde) DeBenedetti 1 04081001620000 37.40156 -122.40795 21-6S-5W San Mateo 1405-1420 Purisima Pliocene -22.11 -21.74 Chevron LL-2, DE-3, Fm-3, Age-3M1 45 Half Moon Bay area Cowell 1 (Mid-St Consolidated) 04081000900000 Northwest of Verde producing area of field. 37.42199 -122.43236 8-6S-5W San Mateo -22.49 -21.10 Chevron SampID-4, LL-API-2,STR-2

M2 46 Antelope Hills Phippen 18 04029618790000 Moderately biodegraded. 35.51158 -119.84815 8-28S-20E Kern 2295-2460 Button Bed (IB) sand Middle Miocene -22.99 -22.34 MacKevett, Nat LL-1M2 47 Belridge, South Sec 13 88-A 04029297650000 Moderately biodegraded. 35.48505 -119.76203 13-28S-20E Kern 0-1500 Etchegoin/Gusher Pliocene -22.98 -22.22 Peters, Ken (Chevron) Field-2, LL-1, API-1M2 48 Edison Ryan Brown 4B 04029065460000 Heavily biodegraded. 35.37200 -118.86729 28-29S-29E Kern Chanac Pliocene -23.09 -22.73 Peters, Ken (Chevron) LL-1, API-1M2 49 Half Moon Bay (Purisima Ck.) Layne 2 (John Tedesco) 04081000160000 37.41511 -122.39804 15-6S-5W San Mateo 710 Purisima Pliocene -23.67 -23.08 Haglund, Dave (Shell) LL-2M2 50 Hollister- Flint Hills area Justo 1 04069000500000 Petrolex Inc operator. 36.86477 -121.41718 28-12S-5E San Benito Etchegoin (?) Pliocene (?) -22.24 -20.63 Chevron Field-2, LL-2, API-2, STR-2, Fm-7, Age-7M2 51 Kern Front Fee 10-11 04029106620000 Heavily biodegraded. 35.45659 -119.04887 27-28S-27E Kern Chanac Pliocene -23.37 -22.52 Peters, Ken (Chevron) LL-1, API-1M2 52 King City BCB Doud 4-32 04053009970000 Heavily biodegraded. 36.15286 -121.12717 32-20S-8E Monterey 2000 Monterey/Thorup zone Miocene -22.99 -22.43 Abel, Pat (CDOGG) LL-2M2 53 La Honda Lane Union Oil 4 04081000730000 Well name formerly Neaves Union Lane 4. 37.32188 -122.31536 17-7S-4W San Mateo 1800-2277 Butano/Costa Eocene -23.14 -22.19 Chevron SampID-2, LL-2, DE-3, Fm-3, Age-3M2 54 La Honda, South Neaves Union Burns 8 04081000610000 Moderately biodegraded. Producing formation is informal name. 37.30524 -122.29546 21-7S-4W San Mateo 1358-1468 Burns sand Lower Miocene -22.42 -21.86 Haglund, Dave (Shell) LL-2, Age-7M2 55 La Honda, South Neaves-Burns Well # unknown, location center of sec 21. Heavily biodegraded. 37.3076 -122.3042 21-7S-4W San Mateo Burns sand (?) Lower Miocene (?) -22.84 -22.49 Chevron Field-4, LL-5, Fm-3M2 56 Petaluma tank battery oil in NE1/4 of sec 30 04097000080000 Specific well unknown, use Petaluma Community 5-2 location. 38.25549 -122.55575 30-5N-6W Sonoma 920 avg. Petaluma Pliocene -22.96 -22.23 Magoon, Les (USGS) LL-2M2 57 Petrolia Hidden Valley 1 04023200270000 Well shut in. 40.37421 -124.29039 21-1S-2W Humboldt 1185-1363 Franciscan Eocene to Cretaceous -23.51 -22.56 McLaughlin, Robert (USGS) LL-6M2 58 Petrolia Hidden Valley 1 04023200270000 Well shut in. 40.37421 -124.29039 21-1S-2W Humboldt 1185-1363 Franciscan Eocene to Cretaceous -23.30 -23.31 Lillis & others (USGS) LL-6M2 59 Petrolia Shelby Woods 1 04023000970000 Well shut in. 40.37369 -124.28996 21-1S-2W Humboldt 700-1394 Franciscan Eocene to Cretaceous -23.31 -23.28 Lillis & others (USGS) LL-6M2 60 Petrolia Shelby Woods 1 04023000970000 Chevron sample collection. 40.37369 -124.28996 21-1S-2W Humboldt 1365-1394 Franciscan Eocene to Cretaceous -23.31 -23.19 Chevron SampID-4, LL-6, Fm-7, Age-7M2 61 Petrolia Whitchurch 1A 04023200650000 Sample 1 of 3. Well shut in. 40.37596 -124.28962 16-1S-2W Humboldt 726-760 Franciscan Eocene to Cretaceous -23.37 -23.18 Lillis & others (USGS) LL-6M2 62 Petrolia Whitchurch 1A 04023200650000 Sample 3 of 3. Well shut in. 40.37596 -124.28962 16-1S-2W Humboldt 726-760 Franciscan Eocene to Cretaceous -23.27 -23.22 Lillis & others (USGS) LL-6M2 63 Pinole Point Bethlehem 1 04013200430000 37.99988 -122.34032 19-2N-4W Contra Costa 6400 Neroly/lower zone Upper Miocene -22.36 -21.53 Tedesco, Larry (Chevron) LL-2M2 64 San Ardo Alexander 23 04053206600000 Heavily biodegraded. 35.94882 -120.81090 8-23S-11E Monterey Monterey/Aurignac sand Miocene -23.38 -22.74 Abel, Pat (CDOGG) LL-2M2 65 San Ardo Hambey 46-18 04053001620000 Heavily biodegraded. 35.93439 -120.82957 18-23S-11E Monterey 2300 Monterey/Lombardi sand Miocene -23.40 -22.21 Abel, Pat (CDOGG) LL-2M2 66 Sargent 10 (no lease name) 04085000370000 Moderately biodegraded. 36.93113 -121.58987 36-11S-3E Santa Clara Etchegoin (?) Pliocene (?) -24.26 -23.57 Chevron LL-2, API-2, Fm-7, Age-7M2 67 Sargent Gulf-James W. Rea Jr. et. al. M-1 04085000480001 Well formerly named McMillan M-1. Heavily biodegraded. 36.92974 -121.58526 36-11S-3E Santa Clara Etchegoin (?) Pliocene (?) -24.52 -23.93 Chevron LL-2, API-2, STR-2, Fm-7, Age-7M2 68 Sargent tank battery oil 04085200330000 Moderately biodegraded. Specific well known, use Sargent #2. 36.92923 -121.58663 36-11S-3E Santa Clara 600 avg Etchegoin (?) Pliocene (?) -24.10 -23.64 Abel, Pat (CDOGG) LL-2, SampID-7, DE-7, Fm-7, Age-7M2 69 seep - Tarwater Creek Tarwater Creek Seep Severely biodegraded. 37.26823 -122.23937 6-8S-3W San Mateo Purisima Pliocene -22.62 -21.88 Magoon & Lorenson (USGS) LL-5, Fm-8, Age-8M2 70 stain - Majors Creek Majors Creek Oil-stained sandstone. Severely biodegraded. 36.98278 -122.14216 12-11S-3W Santa Cruz Elev. 160 Santa Cruz Mudstone Miocene -23.30 -22.10 Lillis, Paul (USGS) LL-5M2 71 stain - Majors Creek area 98SM-1 Point Quarry Bituminous sandstone. Projected SecTwnRng. 37.00681 -122.10889 6-11S-2W Santa Cruz Elev. 880 Santa Cruz Mudstone Miocene -22.77 -22.05 Stanley, Rick (USGS) LL-5M2 72 stain - Majors Creek area 98SM-2 Point Quarry Asphalt in fractured mudstone. Projected SecTwnRng. 37.00681 -122.10889 6-11S-2W Santa Cruz Elev. 880 Santa Cruz Mudstone Miocene -23.05 -22.06 Stanley, Rick (USGS) LL-5M2 73 stain - Majors Creek area 98SM-3 Coast Road Asphalt in fractured dolomite concretion. Projected SecTwnRng. 36.98417 -122.14750 11-11S-3W Santa Cruz Elev. 120 Santa Cruz Mudstone Miocene -22.91 -22.69 Stanley, Rick (USGS) LL-5M2 74 stain - Majors Creek area 98SM-4 Back Ranch Rd Bituminous sandstone. Projected SecTwnRng. 36.99042 -122.13722 12-11S-3W Santa Cruz Elev. 520 Santa Cruz Mudstone Miocene -23.02 -22.09 Stanley, Rick (USGS) LL-5M2 75 stain - Majors Creek area 98SM-5 Hwy 1/Back Ranch Rd Bituminous sandstone. Projected SecTwnRng. 36.98292 -122.14222 12-11S-3W Santa Cruz Elev. 160 Santa Cruz Mudstone Miocene -22.85 -22.10 Stanley, Rick (USGS) LL-5M2 76 stain - Yellow Bank Creek 98SM-6 Yellow Bank Creek Oil?-stained sandstone. Projected SecTwnRng. 36.99139 -122.16806 10-11S-3W Santa Cruz Elev. 20 Santa Cruz Mudstone Miocene -24.01 -23.26 Stanley, Rick (USGS) LL-5M2 77 stain - Point Arena Point Arena Cove Oil-stained sandstone. Severely biodegraded. 38.91639 -123.71139 11-12N-17W Mendocino Elev. 25 Point Arena Formation Miocene -23.40 -22.70 Stanley, Rick (USGS) LL-5M2 78 stain - Point Montara CS -1 Oil-stained sandstone. Severely biodegraded. 37.53733 -122.51767 33-4S-6W San Mateo Elev. 25 marine terrace Pleistocene -21.35 -20.57 Stevens, Cal (San Jose State) LL-5M2 79 stain - Pt Reyes PR-1 Palomarin Beach Sandstone dike, 7cm, visible oil, strong HC odor. 37.92638 -122.73667 ##-1N-8W Marin Elev. 20 Santa Cruz Mudstone Miocene -22.54 -22.37 Stanley, Rick (USGS) LL-6M2 80 stain - Pt Reyes PR-2 Palomarin Beach Sandstone dike, 18in , visible oil. 37.92681 -122.73750 ##-1N-8W Marin Elev. 20 Santa Cruz Mudstone Miocene -22.46 -22.21 Stanley, Rick (USGS) LL-6M2 81 stain - Pt Reyes PR-3 Palomarin Beach Thin ""braided"" sandstone dike, visible. 37.92694 -122.73806 ##-1N-8W Marin Elev. 20 Santa Cruz Mudstone Miocene -22.55 -22.29 Stanley, Rick (USGS) LL-6M2 82 stain - Pt Reyes PR-4 Palomarin Beach Sandstone dike, visible oil, HC odor. 37.92917 -122.74167 ##-1N-8W Marin Elev. 20 Santa Cruz Mudstone Miocene -22.72 -22.20 Stanley, Rick (USGS) LL-6M2 83 stain - Pt Reyes PR-6 Wildcat Beach Sandstone sill or bed, visible oil, HC odor. 37.95278 -122.78236 ##-1N-8W Marin Elev. 20 Santa Cruz Mudstone Miocene -23.17 -22.50 Stanley, Rick (USGS) LL-6M2 84 stain - Pt Reyes PR-7 Wildcat Beach Sandstone sill or bed, visible oil, HC odor. 37.95569 -122.78319 ##-1N-8W Marin Elev. 20 Santa Cruz Mudstone Miocene -23.08 -22.41 Stanley, Rick (USGS) LL-6M2 85 stain - Pt Reyes PR-8 Wildcat Beach Sandstone sill or bed, visible oil, HC odor. 37.95778 -122.78403 ##-1N-8W Marin Elev. 20 Santa Cruz Mudstone Miocene -22.90 -22.52 Stanley, Rick (USGS) LL-6M2 86 stain - Pt Reyes PR-9 Wildcat Beach Sandstone sill or bed with visible oil. 37.96125 -122.78625 ##-1N-8W Marin Elev. 20 Santa Cruz Mudstone Miocene -22.93 -22.20 Stanley, Rick (USGS) LL-6M2 87 stain - Pt Reyes PR-27 Wildcat Beach Sandstone, oil-stained. 37.97500 -122.79500 36-2N-9W Marin Elev. 20 Monterey Formation Miocene -23.15 -22.37 Lillis & Stanley (USGS) LL-5M2 88 unnamed field Dr. Peck’s well Production from Dr. Peck’s well.Heavily biodegraded. 37.24514 -121.95832 10-8S-1W Santa Clara 125(?) Monterey (?) Miocene -23.65 -23.14 -23.32 Stanley, Rick (USGS) LL-5M2 89 wildcat well Etter 1 04023000540000 40.24844 -124.13554 36-2S-1W Humboldt 1800-1900 Franciscan (?) Eocene to Cretaceous -23.30 -22.87 Chevron LL-2, Fm-7, Age-7M2 90 wildcat well Pearson USL 1-B 04053211700000 Indian Valley area east of San Ardo field. 36.04636 -120.63676 1-22S-12E Monterey 1982-1997 -23.82 -23.11 Chevron LL-2M3 91 Tompkins Hill Holmes Eureka 16 04023000450000 Condensate. Aromatic data questionable. 40.63436 -124.16260 22-3N-1W Humboldt 3908-4422 Rio Dell Middle Pliocene -24.06 -24.37 Haglund, Dave (Shell) LL-2M3 92 Tompkins Hill tank battery oil Condensate, specific well unknown, use sec22 location. 40.63 -124.16 22-3N-1W Humboldt -24.28 -24.51 Lorenson, Thomas (USGS) LL-2M4 93 seep - Bear River 97PGL-22 Sandstone, oil stained, HC odor. 40.45000 -124.40306 22-1N-3W Humboldt Elev. 20 -24.06 -24.50 Lillis & others (USGS) LL-6M4 94 seep - Bear River 97PGL-23 Fractured rock, 2 oil stains/seeps about 6 ft apart. 40.44667 -124.40472 27-1N-3W Humboldt Elev. 20 -24.76 -23.24 Lillis & others (USGS) LL-6M4 95 seep - False Cape 97PGL-10 Limestone, Oil stained vugs, HC odor. 40.50361 -124.38583 3-1N-3W Humboldt Elev. 20 -22.36 -22.87 Lillis & others (USGS) LL-6M4 96 seep - False Cape 97PGL-7 Sandstone, HC odor. 40.51556 -124.38250 35-2N-3W Humboldt Elev. 20 -23.17 -23.42 Lillis & others (USGS) LL-6M4 97 seep - False Cape 97PGL-3 Mudstone, HC odor. 40.52444 -124.37611 26-2N-3W Humboldt Elev. 20 -24.10 -26.05 Lillis & others (USGS) LL-6M4 98 seep - False Cape 97PGL-4 Sandstone, w oil stained veins, HC odor. 40.52144 -124.37909 26-2N-3W Humboldt Elev. 20 -23.41 -24.44 Lillis & others (USGS) LL-6M4 99 seep - False Cape 97PGL-5 Sandstone, HC odor. 40.51922 -124.38149 26-2N-3W Humboldt Elev. 20 -22.72 -24.25 Lillis & others (USGS) LL-6M4 100 seep - False Cape 97PGL-6 Sandstone, HC odor. 40.51639 -124.38222 35-2N-3W Humboldt Elev. 20 -23.47 -24.36 Lillis & others (USGS) LL-6

X 101 Concord Boylan 1 04013000900000 Condensate. 38.00334 -122.02547 24-2N-2W Contra Costa 2936-3044 F1 zone Upper Cretaceous -28.13 -26.00 Chevron LL-2X 102 Cymric Sauer Dough 25 04029746080000 35.38320 -119.68833 23-29S-21E Kern Phacoides sand Miocene -25.26 -24.07 Peters, Ken (Chevron) LL-1X 103 seep - McLaughlin Mine McLaughlin Gold Mine Heavily biodegraded. Located in NE NE of sec 1. 38.83556 -122.35974 1-11N-5W Napa Elev. 1590 volcanic rock - brecciated zone Pleistocene -25.58 -23.91 Enderlin, Dean (Homestake Mine) LL-5, Comments-4X 104 seep - Oil Creek north 97PGL-2 Sandstone, black, HC odor. 40.52528 -124.37556 26-2N-3W Humboldt Elev. 20 -27.91 -26.82 Lillis & others (USGS) LL-6X 105 seep - Rathbun Rathbun AJ-1000 Severely biodegraded. 39.01970 -122.37758 35-14N-5W Colusa Lower Cretaceous -25.18 -24.07 Elison & Mackevett LL-5X 106 Sherman Island Signal-Upham 1 04067002560000 Condensate. 38.07804 -121.72989 27-3N-2E Sacramento 6300 Martinez/Anderson Paleocene -28.22 -25.56 Haglund, Dave (Shell) LL-2X 107 stain - Mirabel mine Mirabel mine Oil-filled vugs in silica carbonate Hg ore. 38.69917 -122.59611 23-10N-7W Lake Elev. 1360 -24.50 -23.17 Lillis & others (USGS) LL-5X 108 stain - Mirabel mine Mirabel mine curtisite Curtisite - hydrocarbon mineral. 38.69917 -122.59611 23-10N-7W Lake Elev. 1360 nd nd -23.13 Lillis & others (USGS) LL-5X 109 stain - near Helen mine unnamed mine "Paul’s mine" Oil-coated gel in silica carbonate Hg ore. 38.73944 -122.69778 1-10N-8W Lake Elev. 2640 -25.10 -25.59 Lillis & others (USGS) LL-5X 110 Table Bluff (?) Leon-Oro-Blanco T-1 (?) 04023000190000 Questionable sample identification. 40.66742 -124.21832 6-3N-1W Humboldt 4800-4810 -25.74 -24.84 Chevron LL-2X 111 water well Granny Creek H2O Near confluence w/ Mattole River. Possible distillate. 40.26229 -124.19300 28-2S-1W Humboldt -27.30 -27.43 Lillis & Lorenson (USGS) LL-6X 112 wildcat well (?) Etter 1 (?) 04023000540000 Questionable sample from Etter’s barn. Possible distillate cut. 40.24844 -124.13554 36-2S-1W Humboldt -23.51 nd Mary Etter SampID-4, LL-2, rest-7

a. Comments by authors. Biodegradation interpretation based on unpublished gas chromatography data: Mild = n-alkane concentration low or not detected Moderate = acyclic isoprenoid (for example, pristane) concentration low or not detected Heavy = aromatic hydrocarbons (for example, dimethyl napthalenes, methyl phenanthrenes) low or not detected Severe = hopane and sterane concentration low or not detectedb. Latitude and Longitude values are based on NAD 27 datum. c. SecTwnRng = Section Township Ranged. Production Depth or Outcrop Elevation in feet.e. δ13C Sats = saturated hydrocarbons, Arom = aromatic hydrocarbons, Oil-T = oil topped (C15+), Oil-W = whole oil. Reported per mil PDB. 

 nd = not determined due to low concentrationf. The source of sample information is the donator except as noted:

 Data Type LL = latitude and longitude API = API Number DE = Depth/Elevation Fm = Producing Formation/Zone Age = Formation Age SampID = Sample Identification STR = SecTwnRng

Data Source

 1 = IHS Energy  2 = California Division of Oil, Gas and Geothermal Resources website ftp://ftp.consrv.ca.gov/pub/oil/maps/ 3 = California Division of Oil, Gas and Geothermal Resources records 4 = authors modified donator information  5 = authors calculated LL from topographic map 6 = authors measured LL with GPS receiver 7 = authors  8 = California Division of Oil, Gas and Geothermal Resources TR 26
11

Table 2. Stable carbon isotope boundaries of petroleum types from northern and central 

California. Values refer to corners of boxes shown on figure 2. 

 

 

 δ13C δ13C 

 Sats Arom 

 C15+ C15+ 

 

Boundary for Cretaceous -25.70 -24.90 

 -26.80 -23.70 

 -27.90 -24.90 

 -27.00 -26.40 

 

Boundary for Eocene -27.70 -27.47 

 -28.60 -26.46 

 -30.00 -28.00 

 -29.20 -29.12 

 

Boundary for Miocene -21.20 -20.60 

 -22.00 -20.00 

 -24.80 -24.00 

 -24.30 -24.70 
12

Figure 1. Hydrocarbon types in northern California (after Magoon and others, 1995)

-32.0

-30.0

-28.0

-26.0

-24.0

-22.0

-20.0

-32.0 -30.0 -28.0 -26.0 -24.0 -22.0 -20.0

δ13C Saturated Hydrocarbons

δ13C Aromatic Hydrocarbons

Monterey - S. Calif

Group 1- Miocene

Group 2- Cretaceous

Group 4- Eocene

Group 1 - Miocene

Group 2 - Cretaceous

Group 4 - Eocene

Group 3 - Condensates (not plotted)
13

non-waxy oils (marine)

waxy oils (non-marine)

Sofer (1984)

107

110

101

106

102

103

109

105

104

-30.0

-29.0

-28.0

-27.0

-26.0

-25.0

-24.0

-23.0

-22.0

-21.0

-20.0

-31.0 -30.0 -29.0 -28.0 -27.0 -26.0 -25.0 -24.0 -23.0 -22.0 -21.0 -20.0

δ13C Saturated Hydrocarbons

δ13C Aromatic Hydrocarbons

Miocene M1

Miocene M2

Miocene M3

Miocene M4

Eocene

Cretaceous K1

Cretaceous K2

Cretaceous K3

Cretaceous K4

unclassified

Miocene

Cretaceous

Eocene

Petrolia

Figure 2. Isotopic composition of oils, oil seeps, and oil stains, northern California. See table 2 for oil boundary coordinates.