Mineral Resources of the Southern Otay 

Mountain and Western Otay Mountain 

Wilderness Study Areas, San Diego 

County, California

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Chapter E

Mineral Resources of the Southern Otay 

Mountain and Western Otay Mountain 

Wilderness Study Areas, San Diego 

County, California

By VICTORIA R. TODD, GREGORY K. LEE, and 

HOWARD W. OLIVER 

U.S. Geological Survey

J. DOUGLAS CAUSEY and STEVEN W. SCHMAUCH 

U.S. Bureau of Mines

U.S. GEOLOGICAL SURVEY BULLETIN 1711

MINERAL RESOURCES OF WILDERNESS STUDY AREAS:

SOUTHERN CALIFORNIA AND CALIFORNIA DESERT CONSERVATION AREA
DEPARTMENT OF THE INTERIOR 

DONALD PAUL MODEL, Secretary

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director

Any use of trade names and trademarks 

in this publication is for descriptive 

purposes only and does not constitute 

endorsement by the U.S. Geological Survey

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1988

For sale by the

Books and Open-File Reports Section

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Library of Congress Cataloging-in-Publication Data

Mineral resources of the Southern Otay Mountain and 

Western Otay Mountain Wilderness Study Areas, San 

Diego County, California.

(Mineral resources of wilderness study areas southern 

California and California Desert Conservation Area ; 

ch. E) (U.S. Geological Survey bulletin ; 1711)

Supt. of Docs. no. : I 19.3:1711-E

Bibliography: p.

1. Mines and mineral resources California Southern 

Otay Mountain Wilderness. 2. Mines and mineral resources 

 California Western Otay Mountain Wilderness.

3. Southern Otay Mountain Wilderness (Calif.)

4. Western Otay Mountain Wilderness (Calif.)

I. Todd, Victoria R. (Victoria Roy) II. U.S.

Geological Survey. III. Series. IV. Series: U.S.

Geological Survey bulletin ; 1711.

QE75.B9 no. 1711-E 557.3 s 88-600123

[TN24.C2] [553'.09794'98]
STUDIES RELATED TO WILDERNESS

Bureau of Land Management Wilderness Study Areas

The Federal Land Policy and Management Act (Public Law 94-579, October 21, 1976) requires the 

U.S. Geological Survey and the U.S. Bureau of Mines to conduct mineral surveys on certain areas to 

determine the mineral values, if any, that may be present. Results must be made available to the public 

and be submitted to the President and the Congress. This report presents the results of mineral surveys for 

the Southern Otay Mountain (CA-060-029) and Western Otay Mountain (CA-060-028) Wilderness Study 

Areas, San Diego County, California.

CONTENTS

Summary El

Abstract 1

Character and setting 1

Identified mineral resources 1

Mineral resource potential of the Southern Otay Mountain Wilderness Study Area 2

Mineral resource potential of the Western Otay Mountain Wilderness Study Area 3 

Introduction 3

Description of areas 3

Previous and present investigations 3

Acknowledgments 5

Regional geologic setting 5 

Appraisal of identified resources 5

Mines, prospects, and mineralized areas 5

Appraisal of mineral resources 6 

Assessment of mineral resource potential 6

Geology 6

Geochemical studies 8

Geophysical studies 9

Conclusions for the Southern Otay Mountain Wilderness Study Area 12

Conclusions for the Western Otay Mountain Wilderness Study Area 13 

References cited 13 

Appendixes

Definition of levels of mineral resource potential and certainty of assessment 16

Resource/reserve classification 17

Geologic time chart 18

FIGURES

1. Index map showing location of Southern Otay Mountain and Western Otay Mountain Wilderness 

Study Areas, San Diego County, California E2

2. Map showing mineral resource potential and generalized geology of Southern Otay Mountain and 

Western Otay Mountain Wilderness Study Areas, San Diego County, California 4

3. Isostatic gravity residual map of Southern Otay Mountain and Western Otay Mountain Wilderness 

Study Areas, California 10

4. Residual total-intensity aeromagnetic map and profile A-A' of Southern Otay Mountain and Western 

Otay Mountain Wilderness Study Areas, California 11

TABLE

1. Mines, claims, and prospects in and adjacent to the Southern Otay Mountain and Western Otay 

Mountain Wilderness Study Areas, California E7

Contents V

MINERAL RESOURCES OF WILDERNESS STUDY AREAS:

SOUTHERN CALIFORNIA AND CALIFORNIA DESERT CONSERVATION AREA

Mineral Resources of the Southern Otay 

Mountain and Western Otay Mountain 

Wilderness Study Areas, San Diego 

County, California

By Victoria R. Todd, Gregory K. Lee, and Howard W. Oliver 

U.S. Geological Survey

J. Douglas Causey and Steven W. Schmauch 

U.S. Bureau of Mines

SUMMARY

Abstract

At the request of the U.S. Bureau of Land Management, 

approximately 7,940 acres of the Southern Otay Mountain 

Wilderness Study Area (CA-060-029) and 5,750 acres of the 

Western Otay Mountain Wilderness Study Area (CA-060-028) 

were evaluated for identified mineral resources (known) and 

mineral resource potential (undiscovered); any mention of the 

study areas in this report refers only to those areas for which 

mineral surveys were made. The study areas, in southwest 

San Diego County, Calif., are contiguous and have similar 

geology and mineral resources. Several mines, prospects, 

and claims are present in the study areas, but none are being 

actively mined; only one, the Border View claims, is being 

actively prospected. No mineral resources were identified in 

the Southern Otay Mountain or Western Otay Mountain 

Wilderness Study Areas. An area in the northeastern part of 

the Southern Otay Mountain Wilderness Study Area has low 

potential for undiscovered gold resources, and the 

northwestern part of the Western Otay Mountain Wilderness 

Study Area has low potential for undiscovered gold and lead 

resources. There is no potential for oil, gas, coal, or 

geothermal resources in the study areas.

Character and Setting

The Southern Otay Mountain and Western Otay 

Mountain Wilderness Study Areas are located in the rugged 

San Ysidro Mountains only 13 to 21 mi inland from the 

Pacific Ocean (fig. 1). Maximum relief in the southern and 

western study areas is about 3,150 and 2,800 ft,

Publication authorized by the Director, U.S. Geological Survey, Feb. 25, 1988.

respectively. The United States-Mexico border forms the 

south boundary of the Southern Otay Mountain Wilderness 

Study Area. The areas have a mild, semiarid climate and 

a dense cover of chapparal.

The study areas are underlain by the Santiago Peak 

Volcanics of Late Jurassic age (see appendixes for geologic 

time chart), which are part of a northwest-trending belt of 

Upper Jurassic and Lower Cretaceous volcanic and 

sedimentary rocks that extends for at least 400 mi from 

southern California, U.S.A., down the peninsula of Baja 

California, Mexico. These rocks were intruded on the east 

by the Peninsular Ranges batholith of Cretaceous age and 

are overlain unconformably on the west by Tertiary and 

Quaternary sedimentary deposits.

Identified Mineral Resources

No mineral resources were identified in the Southern 

Otay Mountain or Western Otay Mountain Wilderness 

Study Areas. Gold was found in the 19th century in the 

Mine Canyon area of the Dulzura (Oneida) mining district 

adjacent to the east boundary of the Southern Otay 

Mountain Wilderness Study Area (fig. 2). Production from 

mines and claims in the Mine Canyon area outside the 

study area was minor; none of the properties are presently 

active. Gold was detected in minor amounts in rock 

samples from six of eight prospects within, or near the 

boundary of, the study area.

There has been no mining activity in the Western Otay 

Mountain Wilderness Study Area. The Cedar Creek 

deposit, which contains sphalerite and galena, lies about 1 

mi east of the northeast boundary of the study area. 

Samples from three prospects within the study area 

contained no significant metallic or nonmetallic values.

Mineral Resources of the Southern Otay Mountain and Western Otay Mountain Wilderness Study Areas, California El
Mineral Resource Potential of the Southern 

Otay Mountain Wilderness Study Area

Geologic, geochemical, and geophysical studies 

indicate low potential for undiscovered gold resources in 

the northeast part of the study area (fig. 2). Volcanic rocks 

of Late Jurassic age in the study area underwent low-grade 

metamorphism and hydrothermal alteration marked by 

widespread silicification and pyritization, probably during 

the late stages of emplacement of the Peninsular Ranges 

batholith during the Cretaceous period. The deposition of

gold was localized in and near the Mine Canyon fault. 

Slightly anomalous concentrations of gold, and other 

possibly ore-related elements such as silver, tungsten, zinc, 

antimony, and arsenic, in sediments and rock samples from 

streams that drain the easternmost part of the study area 

suggest that small amounts of undiscovered minor precious 

metals (gold and silver) may be present in that part of the 

study area. The part of the study area between Mine 

Canyon and a north-northwest-trending drainage divide 

about 1 mi to the west has low potential for undiscovered 

gold resources. There is no potential for oil, gas, coal, or 

geothermal resources in the study area.

Rancho Santa Fe

WESTERN OTAY MOUNTAIN

WILDERNESS STUDY AREA

(CA-O60-028)

SOUTHERN OTAY MOUNTAIN

WILDERNESS STUDY AREA

(CA-O60-029)

Figure 1. Index map showing location of Southern Otay Mountain and Western Otay Mountain Wilderness Study Areas, San 

Diego County, California.

E2 Mineral Resources of Wilderness Study Areas Southern California and California Desert Conservation Area
Mineral Resource Potential of the Western 

Otay Mountain Wilderness Study Area

Geochemical studies indicate low potential for 

undiscovered gold and lead resources in the northwest part 

of the Western Otay Mountain Wilderness Study Area (fig. 

2). Heavy-mineral panned concentrates of sediment from 

two streams that drain this part of the study area contained 

detectable gold and anomalous concentrations of lead. 

There is no potential for oil, gas, coal, or geothermal 

resources in the study area.

INTRODUCTION 

Description of Areas

This mineral survey was requested by the U.S. Bureau 

of Land Management (BLM) and is the result of a 

cooperative effort by the U.S. Geological Survey (USGS) 

and the U.S. Bureau of Mines (USBM). An introduction to 

the wilderness review process, mineral survey methods, 

and agency responsibilities was provided by Beikman and 

others (1983). The U.S. Bureau of Mines evaluates 

identified resources at individual mines and known 

mineralized areas by collecting data on current and past 

mining activities and through field examination of mines, 

prospects, claims, and mineralized areas. Identified 

resources are classified according to a system that is a 

modification of that described by McKelvey (1972) and 

described by the U.S. Bureau of Mines and the U.S. 

Geological Survey (1980). Studies by the U.S. Geological 

Survey are designed to provide a reasonable scientific basis 

for assessing the potential for undiscovered mineral 

resources by determining geologic units and structures, 

possible environments of mineral deposition, presence of 

geochemical and geophysical anomalies, and applicable 

ore-deposit models. Mineral assessment methodology and 

terminology as they apply to these surveys were discussed 

by Goudarzi (1984). See appendixes for the definition of 

levels of mineral resource potential and certainty of 

assessment and for the resource/reserve classification.

This report presents the results of mineral surveys of 

the Southern Otay Mountain (CA-060-029) and Western 

Otay Mountain (CA-060-028) Wilderness Study Areas. 

The areas studied in the Southern Otay Mountain and 

Western Otay Mountain Wilderness Study Areas include 

about 7,940 and 5,750 acres, respectively, in southwest San 

Diego County, about 20 mi southeast of San Diego (fig. 1). 

The study areas, separated only by a 1/8-mi-wide strip of 

land, have similar geology and mineral resources. They are 

located in the San Ysidro Mountains, a rugged foothill 

range of the southern California Peninsular Ranges, that lie 

about 13 to 21 mi inland from the Pacific Ocean. 

Elevations in the Southern Otay Mountain Wilderness 

Study Area range from about 400 ft in the Tijuana River

valley to 3,551 ft on a peak located south of the Otay 

Mountain Truck Trail about 1 mi east of its junction with 

the Minnewawa Truck Trail (fig. 2). In the Western Otay 

Mountain Wilderness Study Area, elevations range from 

about 600 ft near Jamul Valley to about 3,400 ft just north 

of the summit of Otay Mountain (fig. 2). The southern 

latitude of the San Ysidro Mountains and their proximity to 

the ocean result in a mild climate with summer daytime 

temperatures ranging from 80 to 90 °F and average annual 

precipitation (mainly as rain in the winter) of about 10 in. 

The mild climate fosters reptilian wildlife and a nearly 

impenetrable growth of chaparral.

The Southern Otay Mountain Wilderness Study Area is 

bounded on the north and west by the Otay Mountain Truck 

Trail, on the south by the Mexican border, and on the east 

by Mine Canyon and Marron Valley (fig. 2). The Western 

Otay Mountain Wilderness Study Area is bounded on the 

east by the Minnewawa Truck Trail, on the southeast and 

south by the Otay Mountain Truck Trail, and on the west 

and north by private land. The Otay Mountain Truck Trail 

lies between the study areas. Access to the study areas is 

from California State Highway 94 to Marron Valley road, 

on the east side of the range, and from California State 

Highway 117 through Kuebler Ranch to the Otay Mountain 

Truck Trail on the west side (fig. 1). There is a locked gate 

on Minnewawa Truck Trail at its intersection with the Otay 

Lakes Road on the north side of the range. Other jeep 

trails, pack trails, and firebreaks make the study areas 

accessible by foot.

Previous and Present Investigations

Detailed geologic studies have not been made in the 

San Ysidro Mountains. Published geologic maps include 

the San Diego-El Centre 1° x 2° quadrangle by Strand 

(1962) and the Otay Mesa 7.5' quadrangle by Kennedy and 

Tan (1977); the latter includes the westernmost part of the 

San Ysidro Mountains. Weber (1963) briefly described the 

geology of the San Ysidro Mountains in a report on the 

mineral resources of San Diego County. The USGS carried 

out rock and stream-sediment sampling for geochemical 

analysis in 1985, reconnaissance field mapping in 1986, 

and aeromagnetic and gravity surveys in 1987. Samples of 

25 stream sediments, 22 heavy-mineral panned 

concentrates, and 22 rocks were collected and analyzed.

The U.S. Bureau of Mines conducted a library search 

for information on mines and prospects in and near the 

study areas. Descriptions of mining activity in the Dulzura 

(Oneida) mining district in and adjacent to the Southern 

Otay Mountain Wilderness Study Area are found in Storms 

(1893), Crawford (1896), Merrill (1916), Tucker (1925), 

and Tucker and Reed (1939). Library research included 

USBM files and MILS (Mineral Industry Location 

System). Claim location data were taken from BLM 

mining claim recordation indices, BLM land status and use

Mineral Resources of the Southern Otay Mountain and Western Otay Mountain Wilderness Study Areas, California E3
116° 55' 116° 50' 116°

\ ^xASj. T>

L [ft Cedar Creek \a : Donohoe Mm/ £==-/ dep°fi v _2?]\ A <;

Jsp ^

L/B Au,Pl>

APPROXIMATE BOUNDARY OF

__ .

APPROXIMATE BOUNDARY OF

SOUTHERN OTAY MOUNTAIN

WILDERNESS STUDY AREA

(CA-060-029)

EXPLANATION

Area having low mineral resource potential (L) for 

commodities as shown; data only suggest 

certainty level (B) QTs

Commodities

Au Gold 

Pb Lead

Mines, claims, and prospects See table 1 for 

description

1. Unnamed prospect

2. Silver Queen claim

3. Bonanza claim

4. Johnston mine

5. Doolittle group

6. Unnamed prospect

7. Donohoe mine

8. W & T claims

9. Border View Nos. 1-4 claims

10. Ocean View claims

11. Otay Mining Company claim

Kgr 

KJg 

Jsp

Description of map units

Sedimentary deposits (Quaternary and Tertiary) Includes 

unnamed fanglomerate deposits, Rosarito Beach 

Formation, Lindavista Formation, and surficial deposits

Undifferentiated granitic rocks (Cretaceous) Part of 

Peninsular Ranges batholith

Gabbro (Cretaceous and(or) Jurassic) Hypabyssal pluton; 

may be part of Peninsular Ranges balholith

Santiago Peak Volcanics (Jurassic)

Contact Dotted where concealed

High-angle fault Dashed where approximately located or 

inferrred, dotted where concealed. Arrows indicate sense 

of lateral displacement, querried where uncertain

Stream

Stream-sediment sample site Panned-concentrate and(or) 

rock samples also taken at some sites. Numbered if noted 

in text

Rock sample site

Mine See table 1 for description

Prospect, claim See table 1 for description

Figure 2. Mineral resource potential and generalized geology of Southern Otay Mountain and Western Otay Mountain 

Wilderness Study Areas and vicinity, San Diego County, California. Rock and stream-sediment sample analyses reported by 

Causey and Schmauch (1987) and G.K. Lee (unpub. data, 1985).

E4 Mineral Resources of Wilderness Study Areas Southern California and California Desert Conservation Area
records, and county claim records. In 1986, USBM 

personnel mapped and sampled workings in and near the 

study areas and collected 85 rock samples for chemical 

analysis by fire assay, atomic-absorption, or colorimetric 

methods. Heavy-mineral separates from two alluvial 

samples were examined optically. All samples were 

examined for radioactivity and fluorescence. A summary 

of analytical results is in Causey and Schmauch (1987); 

significant results are noted in table 1. Complete results are 

on file at the USBM, Western Field Operations Center, 

East 360 Third Avenue, Spokane, WA 99202.

Acknowledgments

The authors thank W.A. Dean of Poway, Calif., for 

claim information and drill-sample splits. We also thank 

personnel of the Bureau of Land Management for advice on 

access to the study areas and for generously making their 

records available to us.

Regional Geologic Setting

The Southern Otay Mountain and Western Otay 

Mountain Wilderness Study Areas are underlain by 

metavolcanic rocks that are assigned to the Upper Jurassic 

Santiago Peak Volcanics (Larsen, 1948). The Santiago 

Peak Volcanics are part of a discontinuous, northwesttrending, 10-mi-wide belt of Upper Jurassic and Lower 

Cretaceous volcanic and sedimentary rocks that lies within 

a few miles of the Pacific coast and extends for at least 400 

mi from southern California, U.S.A., down the peninsula of 

Baja California, Mexico. These rocks were intruded on the 

east by the predominantly granitic Peninsular Ranges 

batholith in Late Jurassic to middle Cretaceous time. They 

are partly overlain on the west by Upper Cretaceous, 

Tertiary, and Quaternary sedimentary deposits. Field 

relations along the length of the volcanic belt suggest that 

the westernmost, oldest plutons of the batholith were 

feeders for the overlying volcanic rocks (Todd and others, 

in press).

Although not studied in detail, the metavolcanic rocks 

of the San Ysidro Mountains are similar to well-studied 

volcanic and volcaniclastic sequences elsewhere in San 

Diego County and northernmost Mexico. Volcanic rocks 

35 mi to the northwest near Rancho Santa Fe are andesitic 

to rhyolitic flows and tuffs with minor basalt (Adams, 

1979). Intercalated with these fine-grained rocks are 

variable amounts of breccia, agglomerate, and volcanic 

conglomerate composed of clasts of the same volcanic 

compositions. Balch (1981) and Balch and others (1984) 

described a sedimentary sequence in the Santiago Peak 

Volcanics 3 to 6 mi east of Del Mar that includes 

fossiliferous sandstone, siltstone, and mudstone with sparse

Mineral Resources of the Southern Otay Mountain

tuff layers. Clasts in these rocks are overwhelmingly of 

volcanic origin, and the sequence contains Late Jurassic 

marine fossils that were used to date the unit in southern 

California. Farther to the north, near Camp Pendleton, 

Buesch (1984) described similar volcanic and volcanicderived rocks that were intruded by high-level plutons and 

metamorphosed near the contacts with them. Closer to the 

wilderness study areas and on strike with the metavolcanic 

rocks of the San Ysidro Mountains are low-grade 

metamorphosed andesitic and dacitic tuff and breccia a few 

mi east of San Diego (Todd, unpublished mapping). 

Similar rocks also appear about 7 mi south of the Mexican 

border (Hawkins, 1970).

The Santiago Peak Volcanics are considered to have 

formed in and near an ancient volcanic archipelago built on 

oceanic crust close to the Mesozoic western margin of 

North America (Balch, 1981; Buesch, 1984). The volcanic 

arc was bordered by deep marine basins that received 

alternating volcanic eruptions and sediment fans derived 

from emerging volcanic islands. Soon after eruption and 

deposition, these accumulations were buried, folded, and 

thrust faulted(?), probably during an episode of regional 

deformation that accompanied the earliest intrusions of the 

Peninsular Ranges batholith. As the result of burial, 

heating, and local intrusion, the volcanic and sedimentary 

rocks underwent incipient to low-grade metamorphism. 

This metamorphism is marked by the development of one 

or more metamorphic minerals that include chlorite, illite, 

epidote, albite, calcite, muscovite/sericite, actinolite, 

serpentine, and stilpnomelane.

APPRAISAL OF IDENTIFIED RESOURCES

By J. Douglas Causey and Steven W. Schmauch 

U.S. Bureau of Mines

Mines, Prospects, and Mineralized Areas

The first discovery of gold in the region was in 1828 

when a small placer deposit was reported at San Ysidro 

about 10 mi west of the study areas (Browne and Taylor, 

1867, p. 13). The earliest confirmed mining activity took 

place in 1877 when gold was found in the Mine Canyon 

area (Weber, 1963, p. 63). This area, adjacent to the east 

boundary of the Southern Otay Mountain Wilderness Study 

Area is in the Dulzura (Oneida) mining district. Claims 

located here included the Golden Artery and the Chief of 

the Hills lode claims. A patent survey of these claims in 

1894 reported a 570-ft-long adit, a 100-ft-deep shaft, and 

several open cuts. The ore averaged $8 per ton at $20-peroz price (Storms, 1893, p. 383). Little additional work was 

done on the property after it was patented in 1896. This 

property is now referred to as the Donohoe mine (fig. 2, 

No. 7).

and Western Otay Mountain Wilderness Study Areas, California E5
The Johnston mine and Doolittle group are located 

northwest of the Donohoe mine, also in Mine Canyon. The 

Johnston mine was located in the 1890's and includes a 

330-ft-long adit and several small pits (fig. 2, No. 4). The 

Doolittle group was located in the 1930's and has one small 

pit according to Weber (1963, p. 122 and 143). This group 

probably also includes a nearby adit (fig. 2, Nos. 5 and 6). 

Both properties had limited exploration.

About 1/4 mi south of the Donohoe mine in Mine 

Canyon, 3 oz of gold was recovered from 300 yd3 of gravel 

on the Golden Artery placer claims in 1932 (U.S. Bureau of 

Mines production records).

The most recent claims in the Southern Otay Mountain 

Wilderness Study Area are the Silver Queen and Bonanza 

lode claims (fig. 2, Nos. 2, 3) located along the Otay 

Mountain Truck Trail and the W & T lode claims (fig. 2, 

No. 8) in Mine Canyon. These claims were located in 

1980, 1980, and 1981, respectively. The W & T claims 

partly cover the Golden Artery placer claims. Except for 

two old prospect pits and some gravel piles on the W & T, 

and a small open cut on the Silver Queen, no workings 

were found on these recent claims.

Three prospects are present in the Western Otay 

Mountain Wilderness Study Area. The Border View lode 

claims (fig. 2, No. 9) were located in the 1930's by William 

Dean's father and relocated in the 1970's by William Dean 

and Alfred Landry. Assessment work in the 1980's 

includes trenching, sampling, drilling, and geophysical 

surveying. The Ocean View and Otay Mining Company 

claims (fig. 2, Nos. 10, 11) were located by Alfred Landry. 

All of these claims are southwest of Otay Mountain, along 

a 4-mi section of the Otay Mountain Truck Trail or the 

adjacent bulldozed firebreak areas.

Appraisal of Mineral Resources

No mineral resources were identified in the Southern 

Otay Mountain or Western Otay Mountain Wilderness 

Study Areas. Descriptions of the properties examined in 

the study areas and significant analytical results are given 

in table 1. No property in either study area contained 

significant gold- or silver-bearing rocks, and no other 

metallic or industrial mineral commodities were found. 

Gold-bearing rocks at the Donohoe mine are not known to 

extend into the study area, but they do parallel the border 

on the east side of Mine Canyon.

Small-scale recreational placer mining could occur in 

Mine Canyon on the W & T claims. The gravel deposits 

here have been worked in the past but still contain a small 

amount of gold. The gravel is of limited extent, and the 

gold apparently did not travel far from its source.

No sand and gravel resources were identified in either 

of the study areas. The occurrences are small and scattered 

along narrow stream beds.

ASSESSMENT OF MINERAL RESOURCE 

POTENTIAL

By Victoria R. Todd, Gregory K. Lee, and Howard W. Oliver 

U.S. Geological Survey

Geology

The Southern Otay Mountain and Western Otay 

Mountain Wilderness Study Areas are underlain by a 

sequence of weakly metamorphosed dacitic, andesitic, and 

rhyolitic volcanic rocks assigned to the Santiago Peak 

Volcanics. The rocks are resistant, thinly layered to locally 

massive flows and tuff with minor breccia, agglomerate, 

and volcanic conglomerate. Sandstone, siltstone, and 

mudstone form a minor part of the section. Fresh outcrops 

are typically dark gray to black or greenish gray, 

weathering to tan and reddish- and yellowish-brown colors 

due to the oxidation of iron-bearing sulfide minerals. 

Finely disseminated pyrite is widespread throughout the 

section, and arsenopyrite is a less common replacement 

mineral in mineralized rocks (Weber, 1963, p. 124). Parts 

of the volcanic section have been completely altered to 

quartz-sericite schist and hornfels. Metamorphic 

recrystallization and widespread silicification impede the 

recognition of primary structures; porphyritic and 

fragmental volcanic textures are fairly common, and flow 

banding is seen locally. Some felsitic layers grade from 

silicified metatuff to tuffaceous quartzite and metasiltstone.

Volcanic rocks of the San Ysidro Mountains were 

intruded on the east by the Cretaceous Peninsular Ranges 

batholith, which in this region includes undifferentiated 

granitic rocks and may include gabbro (fig. 2). The gabbro 

pluton shown in figure 2 is chiefly fine grained and is 

partly surrounded by the Santiago Peak Volcanics. 

Because the pluton is undated, it is not known whether it 

was a feeder for the Late Jurassic volcanic rocks or is part 

of the Cretaceous Peninsular Ranges batholith. It is 

possible that high-level plutons such as this one were 

transitional in age and geologic setting between superjacent 

volcanic rocks and deeper level plutons of the batholith.

The volcanic rocks in the southern part of the San 

Ysidro Mountains are cut by fine-grained to aphanitic felsic 

dikes, possibly related to the emplacement of the batholith. 

Although the orientations of the dikes vary, the most 

common trends are northerly and easterly. The dikes 

appear to have utilized north- and east-trending fractures 

and faults. Locally, the slight offset of one dike by a 

second dike of the same set suggests that at least some 

faulting took place during batholithic emplacement. Quartz 

veins and stringers occur locally in mineralized zones.

In Otay Valley, the Santiago Peak Volcanics are 

overlain by Quaternary and Tertiary sedimentary deposits 

(fig. 2). Tertiary deposits on the western and northwestern

E6 Mineral Resources of Wilderness Study Areas Southern California and California Desert Conservation Area
Table 1. Mines, claims,and prospects in and adjacent to the Southern Otay Mountain and Western Otay Mountain Wilderness 

Study Areas, San Diego County, California

[*, outside wilderness study area]

Map No.

(fig. 2) Name Summary Workings and production Sample data

1 Unnamed 

prospect.

2 Silver Queen 

claim.

Bonanza claim 

Johnston mine* 

Doolitde group -

Unnamed 

prospect*

Greenish-gray metamorphosed dacite(?) in 

sequence of metamorphosed mudstone, siltstone, and volcanic rocks.

Metamorphosed volcanic(?) breccia intersected by N. 80° W. shear zone with 

greenish-gray gouge and l/2-in.-thick 

quartz lens.

Bleached metavolcanic rocks with minor iron 

oxide stains adjoin greenish metamorphosed 

volcanic(?) breccia.

Metavolcanic rocks including dacite or 

quartz latite with a few small quartz 

veins are exposed. Northwesterly trending 

shear zones with steep northeast dips 

parallel foliation in country rock. 

Bleaching, silicification, and pyritization prevalent in and near shear zones.

Intensely silicified dacitic(?) tuff containing minor sericite, opalite, opal, 

carbonate minerals, and about 1 percent 

pyrite.

A 1- to 2-ft-thick shear zone strikes 

N. 60° E., dips 50° NW, and cuts green 

homfels containing fine (1/16 in) 

disseminated pyrite (up to 2 percent). 

Quartz crystals line microfractures. 

Probably rock was originally dacite 

or andesite tuff.

One prospect pit 3 ft by 5 ft 

by 3 ft deep.

One prospect pit 20 ft by 135 

ft.

None.

One adit with 330 ft of 

workings. Two small 

prospect pits and two 

shafts.

One prospect pit 5 ft by 

6 ft by 3 ft deep.

One 10-ft-long adit.

One grab sample contained no significant 

values.

Two samples were taken. Chip sample 

contained no significant values; grab 

sample had 5 ppb gold.

One grab sample contained no significant 

values.

Twelve chip samples contained from less 

than 5 to 720 ppb gold. Two samples 

contained 0.2 and 1.1 ppm silver.

Three random chip samples contained 0.2, 

0.8, and 1.1 ppm silver and 20, 45, and 

190 ppb gold.

Two chip samples contained 5 and 10 ppb 

gold.

Donohoe mine* Metamorphosed volcanic rocks including 

(Chief of the dacite, quartz latite, and rhyolite 

Hills, Golden tuffs. Much of rock is very fine 

Artery, Artery grained quartz sericite schist and 

Consolidated, homfels. Fine-grained pyrite is 

Comet, Donohue). disseminated through much of rock. 

Foliation strikes about N. 40° W. and 

dips about 70° NE. No quartz veins are 

evident.

W & T claims 

(incorporates 

area covered by 

Golden Artery 

placer claim).

Border View 

Nos. 1-4 

claims.

10 Ocean View 

claims.

Massive, jointed, heavily iron oxide 

stained metamorphosed volcanic rocks. 

Less than 1 percent pyrite present.

Small, irregularly shaped silicified 

rhyolite dome in contact with layers 

of interbedded latite, homfels, and 

black flow-banded dacite.

Light-brown, decomposed metadacite interbedded with homfels and volcanic breccia.

11 Otay Mining Massive, dark-green, fine-grained metaCompany claim. morphosed tuff. Surfaces weather to 

light brown.

Four adits, one has 700 ft of 

drifts, crosscuts, shafts, and 

slopes; others are 60, 55, and 

7 ft long. Five prospect 

pits, two trenches 23 and 13 

ft long, shaft 21 ft deep, 

millsite foundations, and 

remnants of dam.

One 8-ft-deep shaft, one small 

prospect pit, and several 

sites of worked gravel. 

Placer production from Golden 

Artery was 3 oz gold (U.S. 

Bureau of Mines production 

records).

One shaft 23 ft deep, 15 

prospect pits, and 3 trenches.

Two prospect pits and one 

trench.

One prospect pit

Sixteen chip, twelve grab, and three 

select samples were taken. Twenty-nine 

contained between 0.0006 and 0.089 oz/ton 

gold, and two contained 0.16 and 0.28 

ozAon gold. Ten of these samples 

contained between 0.02 and 0.64 ozAon 

silver, from 3 to 62 ppm copper, 4 to 

8 ppm lead, 15 to 650 ppm zinc, and 

3 to 18 ppm molybdenum. In seven 

samples, tungsten ranged from 3 to 5 

ppm.

Two random chip samples contained 20 ppb 

gold each. Two placer samples, 

collected from beneath large boulders, 

contained 0.0002 and 0.03 oz gold per 

yd?

Twenty-two grab samples and five splits 

from drill-hole cuttings contained no 

significant values.

Three grab samples contained no significant values.

One grab sample contained no significant 

values.

Mineral Resources of the Southern Otay Mountain and Western Otay Mountain Wilderness Study Areas, California E7
flanks of the San Ysidro Mountains include the Rosarito 

Beach Formation (Minch, 1967) and unnamed 

fanglomerate deposits (Kennedy and Tan, 1977). The 

Rosarito Beach Formation is described from a section of 

sedimentary deposits located in northwest Baja California. 

Lithologically similar deposits that underlie Otay Mesa 

west of the study area were previously called the Otay 

Formation or the Otay Member of the Rosarito Beach 

Formation (Kennedy and Tan, 1977; Pinckney and others, 

1979). However, the name Otay Formation or Member has 

been abandoned north of the border and replaced by 

Rosarito Beach Formation (Scheidemann and Kuper, 

1979). In the vicinity of Otay Mesa, the formation consists 

mainly of light-colored, poorly indurated, massive 

sandstone and bentonitic claystone (Kennedy and Tan, 

1977). The formation overlies an unnamed boulderfanglomerate unit that rests unconformably upon the 

Santiago Peak Volcanics to the east and partly interfingers 

with the Rosarito Beach Formation to the west. Clasts in 

this fanglomerate were derived from local bedrock. These 

Tertiary units are overlain unconformably by the late 

Pliocene or early Pleistocene nearshore marine and 

nonmarine Linda vista Formation (Kennedy and Tan, 1977) 

in Otay Valley and by late Pleistocene and Holocene 

stream-terrace, slopewash, and alluvial deposits near the 

Otay Reservoirs and in Jamul and Dulzura Creeks on the 

northwestern flank of the San Ysidro Mountains. 

Significant alluvial deposits are also present in Marron 

Valley, southeast of the Southern Otay Mountain 

Wilderness Study Area. Alluvial deposits within the study 

areas occur mainly in the channels of narrow modern 

streams and are typically thin and discontinuous.

The orientation of layering in the metavolcanic rocks 

of the San Ysidro Mountains varies considerably from west 

to east, possibly because of undetected large-scale folds. In 

the eastern part of the range, layering and foliation trend 

generally northwest and dip moderately to steeply to the 

northeast. In the western part, they trend north-northwest 

to east-northeast and dip gently southwest and north 

(Kennedy and Tan, 1977).

Faults of two main orientations are present in the San 

Ysidro Mountains (fig. 2). The northwest-striking Mine 

Canyon fault in the eastern part of the range parallels the 

northeast boundary of the Southern Otay Mountain 

Wilderness Study Area. This fault coincides approximately 

with the linear array of mines and prospects in the east wall 

of the upper, northwest-trending part of Mine Canyon (fig. 

2). This coincidence suggests that mineralization and 

faulting are related. Small gouge and breccia zones that 

generally parallel foliation in the metavolcanic rocks in the 

Mine Canyon area suggest that the Mine Canyon fault is a 

bedding-plane fault localized in one or more relatively 

unresistant, hydrothermally altered felsitic layers. 

However, geophysical evidence, presented in a later 

section, suggests that the fault may represent the surficial

expression of, or response to, a more significant crustal 

structure. The Mine Canyon fault coincides closely with 

northwest-trending gravity and magnetic gradients that 

continue for at least 12 mi to the northwest (figs. 3 and 44). 

A magnetic profile across the region (fig. 4B) suggests that 

the contact between the Peninsular Ranges batholith and 

metavolcanic rocks of the San Ysidro Mountains dips 

westward and that batholithic rocks are present beneath the 

rocks of the study area.

Numerous east-trending faults, and possibly faultrelated lineaments, cross the range. One of these faults, or 

fault zones, bisects the Southern Otay Mountain Wilderness 

Study Area and crosses the southern part of the Western 

Otay Mountain Wilderness Study Area (fig. 2). A second 

fault crosses the northern part of the Western Otay 

Mountain Wilderness Study Area. Numerous east-trending 

lineaments and felsic dikes occur in the area between the 

southern fault and the Tijuana River. No mining or 

prospecting is known to be associated with the easttrending fault zones. East of the San Ysidro Mountains, the 

partly faulted contact between the Santiago Peak Volcanics 

and the Peninsular Ranges batholith appears to be offset 

left laterally 1 to 2 mi on each of three east-striking faults, 

at least two of which are partly within the map area (fig. 2). 

One of these faults may cut the Mine Canyon fault, 

displacing it left laterally as much as 1 mi.

Northwest- and east-striking joints, faults, and 

megalineaments are common in the Peninsular Ranges 

batholith and are considered to have formed during the 

latest stages of emplacement, uplift, and unroofing of the 

batholith. The above relations suggest that east-trending 

faulting largely postdates the emplacement of the 

Cretaceous batholith and the northwest faulting. Easttrending faults that cut the sedimentary deposits in the area 

south of Lower Otay Reservoir (fig. 2) suggest that this 

faulting was reactivated in the late Tertiary.

The inferred temporal association of faulting, 

silicification, serialization, dissemination of sulfides, and 

gold and silver mineralization in the Mine Canyon area 

suggests that mineralization took place during low- grade 

metamorphism and hydrothermal activity accompanying 

the late stages of emplacement of the batholith. The Mine 

Canyon fault may be the near-surface expression of a 

deeper crustal zone of weakness that developed near the 

contact between the Santiago Peak Volcanics and the 

Peninsular Ranges batholith. Late-stage fluids from the 

crystallizing batholith may have utilized this weak zone as 

a conduit for mineral deposition.

Geochemical Studies

In 1985 a reconnaissance geochemical survey was 

conducted in the Southern Otay Mountain and Western 

Otay Mountain Wilderness Study Areas. For the study, 25

E8 Mineral Resources of Wilderness Study Areas Southern California and California Desert Conservation Area
stream-sediment, 22 heavy-mineral panned-concentrate, 

and 22 rock samples were collected and analyzed. Streamsediment samples were collected from most of the active 

drainages; at each sample site a composite of fine material 

from several localities within the stream was collected. In 

drainages that were large enough to deposit gravel-size 

sediment, heavy-mineral panned concentrates of stream 

sediments were also collected. Most rock samples are 

representative composites of chips from outcrops; at 

locations where altered rocks were found, the most 

mineralized or altered material was preferentially collected.

Stream-sediment samples were dried and sieved 

through an 80-mesh (177-micron) screen, and the fraction 

finer than 80 mesh was analyzed spectrographically by the 

method of Crock and others (1987). Panned concentrates 

were dried, and a small split of each sample was separated 

for spectrographic analysis using the method of Grimes and 

Marranzino (1968). The entire remainder of each 

concentrate was weighed and analyzed for gold content by 

an atomic-absorption spectrophotometric method as 

described by Thompson and others (1968). The rock 

samples were crushed, ground, split, and analyzed by 

spectrographic, atomic-absorption spectrophotometric, and 

induction-coupled plasma-atomic emission spectrometric 

methods (Crock and others, 1987).

Inspection of the statistical distributions of the 

analytical data and consideration of average crustal 

abundances of the elements in comparable lithologic 

terranes (Rose and others, 1979) suggest that at least two 

vicinities in the study areas contain elevated or anomalous 

concentrations of several possibly ore-related minerals. 

Heavy-mineral panned concentrates collected from Mine 

Canyon and its western tributaries generally contained 

detectable gold, although at quite low levels (as much as 

0.10 parts per million). Visible gold was detected in the 

concentrates from two of these locations. Slightly elevated 

silver concentrations were also found at two of the sample 

sites in this vicinity; tungsten and zinc were each present at 

single locations in this part of the study area. The presence 

of accessory ore-related minerals is also indicated by 

elevated values for antimony and arsenic.

These results indicate at least minor precious-metal 

(gold and silver) mineralization in the area lying on the 

west side of Mine Canyon. This mineralization suggests 

that the northwest-trending faults that apparently control 

the gold mineralization just east of Mine Canyon in 

historical mining localities, which include the Donohoe and 

Johnston mines, may also be present farther to the west. 

Because no anomalous concentrations of elements were 

found in samples collected west of Mine Canyon from the 

next major south-flowing tributary of the Tijuana River 

(fig. 2, sample No. 4, O.K. Lee, unpub. data, 1985), it 

seems likely that mineralization is limited to the east side 

of the drainage divide directly west of the Mine Canyon 

basin.

A second vicinity that exhibits geochemical evidence 

of possible mineralization is located in the northwest part 

of the Western Otay Mountain Wilderness Study Area. 

Panned-concentrate samples at two locations just 

downstream from this area (fig. 2, Nos. 26 and 39) 

contained detectable gold and anomalous lead values as 

high as 2,000 ppm. Pyrite and galena and possibly 

anglesite were noted in the concentrate collected at location 

26. Slightly elevated copper (100 ppm) and chromium 

(700 ppm) were also found, although these elements are 

more likely associated with the syngenetic mineralization 

of mafic igneous or metaigneous rocks in the area rather 

than with epigenetic mineralization.

Geophysical Studies

Isostatic gravity residual data and residual totalintensity magnetic data for the San Diego 1° by 2° 

quadrangle have been compiled by H.W. Oliver and others 

(unpub. data, 1988). Regional gravity measurements in the 

San Diego-El Centro area by Biehler (1979) have been 

recompiled in the vicinity of the Southern Otay Mountain 

and Western Otay Mountain Wilderness Study Areas (fig.

3). These data have been corrected for effects of elevation, 

latitude, topography, and regional gradients associated with 

deep crustal structure. Thus, residual variations in gravity, 

as indicated by the gravity contours, provide an insight into 

shallow crustal density variations.

Residual gravity is nearly flat, having a value of about 

-3 mGal (milligal) over the Santiago Peak Volcanics in the 

Western Otay Mountain Wilderness Study Area. Farther 

east, residual gravity rises to a value of +5 mGal at the east 

edge of the Southern Otay Mountain Wilderness Study 

Area and reaches a gravity high of +13 mGal over highdensity gabbroic rocks about 2 mi northeast of the study 

area. The maximum horizontal gradient of about 5 to 6 

mGal/mi on the west flank of the gravity high nearly 

coincides with the Mine Canyon fault. This near 

coincidence indicates that the fault is also the approximate 

surface projection of a boundary between volcanic rocks 

having densities of about 2.7 g/cm3 (grams per cubic 

centimeter) on the west side and denser (3.0 g/cm3 ) 

gabbroic(?) rocks on the east side. On the basis of this 

assumed density contrast of +0.3 g/cm3 and the magnitude 

of the gravity difference of about 16 mGal, the estimated 

depth of the gabbro on the northeast side of the fault is 

about 0.8 mi.

The residual magnetic map and profile (fig. 4) were 

compiled from sparse low-level (approximately 500 ft 

above the terrain) airborne data obtained under the National 

Uranium Resource Evaluation (NURE) program (High Life 

Helicopters, Inc., and QEB, Inc., 1980; U.S. Department of 

Energy, written commun., 1985). The profile crosses the 

Mine Canyon fault about 1 mi north of the study areas (fig.

4). Residual magnetic values range from an ambient level

Mineral Resources of the Southern Otay Mountain and Western Otay Mountain Wilderness Study Areas, California E9
of about -200 nT (nanoteslas) in the vicinity of Lower Otay 

Reservoir, over the approximate contact between the 

Santiago Peak Volcanics and relatively thick Tertiary and 

Quaternary sedimentary deposits to the west, to about 

+1,300 nT within the two magnetic-high closures that form 

a magnetic ridge immediately northeast of, and parallel to, 

the Mine Canyon fault The magnetic ridge also appears to 

be associated with the gabbroic rocks and is displaced 

about 1 mi to the southwest of the gravity high because of 

the effect of the direction of induced magnetization of these 

rocks. This direction parallels the Earth's present magnetic 

field (inclination 61°, declination N. 16° E. in this area).

This magnetic model has been tested quantitatively by 

transforming the magnetic data to pseudogravity data 

assuming magnetic induction in the direction of the present 

field (Baranov, 1957; Blakely and Simpson, 1986). The 

resulting pseudogravity high derived from the magnetic 

data is located directly over the +13 mGal gravity high 

shown in figure 3, and this relation strongly suggests a 

common source for both anomalies. The source rocks must 

be the gabbro, which crops out under the gravity and 

transformed magnetic highs. The near coincidence of the 

maximum horizontal gradients of both the gravity and 

pseudogravity fields with the Mine Canyon fault indicates

116° 55' 116°50' 116°45'

Figure 3. Isostatic gravity residual map of Southern Otay Mountain and Western Otay Mountain Wilderness Study Areas and 

vicinity, California. Corrected for isostatic and topographic effects; assumed density of 2.67 g/cm3 (grams per cubic centimeter) 

for rocks above sea level. Isostatic model is Airy type using sea-level crustal thickness of 25 kilometers (15.5 miles) and crustmantle density contrast of 0.4 g/cm 3 . Contour interval 1 milligal (mGal); hachures indicate closed area of lower gravity. 

Gravity stations shown by small crosses. See figure 2 for explanation of geologic units.

E10 Mineral Resources of Wilderness Study Areas Southern California and California Desert Conservation Area
that the gabbro probably extends westward under the 

Santiago Peak Volcanics, at least to the vicinity of the fault, 

and may be in fault contact with granitic or other less 

dense, less magnetic rocks at depth on the southwest side 

of the fault. The relatively gentle slope and 6-mile extent 

of the flank of the magnetic high west of the Mine Canyon 

fault (C, fig. 46) also suggest that gabbro, perhaps offset 

downward on the west side of the fault, extends for some 

distance to the west of the fault beneath the Santiago Peak 

Volcanics.

This magnetic interpretation is complicated by the 

slightly magnetic character of the Santiago Peak Volcanics 

as evidenced by the magnetic highs marked A and B in 

figure 48. Magnetic highs are located approximately at the 

west edge of outcrop of the volcanic rocks (A) and at a 

topographic ridge in the volcanic rocks (B). The main 

high, D, located over a small ridge on the east side of 

Sycamore Canyon (fig. 4A), is displaced slightly to the 

southwest of the gabbro body, as discussed above. The 

gabbro pluton that crops out east of the study areas is part

116° 55' 116° 50' 116°45'

Figure 4. Residual total-intensity aeromagnetic data for Southern Otay Mountain and Western Otay Mountain Wilderness Study 

Areas and vicinity, San Diego County, California. See figure 2 for explanation of geologic units. A, Map of area contoured 

from 0.3-mile (E-W) by 0.6-mile (N-S) gridded data; contour interval 100 nanoteslas (nT) (1 nT=1 gamma); hachures indicate 

closed area of lower aeromagnetic intensity. Flightlines shown by small crosses. 6, Profile A-A' along flightline. Details and 

extremes of profile do not show on map because E-W grid interval of map is coarser than digital readout (3 seconds or about 

0.1 mile) along profile.

Mineral Resources of the Southern Otay Mountain and Western Otay Mountain Wilderness Study Areas, California E11
of a northwest-trending linear array of gabbro plutons that 

extends for about 20 mi from the Mexican border to El 

Cajon (fig. 1) near the contact of the Santiago Peak 

Volcanics and the Peninsular Ranges batholith (Strand, 

1962).

Conclusions for the Southern Otay Mountain 

Wilderness Study Area

Geologic, geochemical, and geophysical investigations 

in and near the Southern Otay Mountain Wilderness Study 

Area suggest that the northeastern part of the study area 

may contain undiscovered gold resources. Historically, 

mining has been confined largely to the fault in the east

wall of Mine Canyon just outside the study area. Slightly 

anomalous concentrations of gold and other possibly orerelated elements such as silver, tungsten, zinc, antimony, 

and arsenic in rocks and stream sediments from drainages 

in the west wall of the canyon suggest that mineralization 

also took place within the study area. Silicification and 

pyritization are widespread in the low-grade metavolcanic 

rocks of the study area, but significant mineralization 

appears to be confined to the area in and near Mine 

Canyon. The part of the study area located between Mine 

Canyon and a prominent north-northwest-trending drainage 

divide about 1 mi to the west has low potential, certainty 

level B, for undiscovered gold resources. See appendixes 

for definition of levels of mineral resource potential and 

certainty of assessment.

A'

1,600

1,400

1,200

1,000

800

Main high over small ridge on 

east side of Sycamore Canyon

D

Topographic ridge in 

volcanic rocks

600

400

200

Approximate west edge of outcrop 

of Santiago Peak Volcanics

-200

567 

DISTANCE, IN MILES

Figure 4. Continued.

E12 Mineral Resources of Wilderness Study Areas Southern California and California Desert Conservation Area

10 11
There is no potential for oil, gas, coal, or geothermal 

resources in the study area, certainty level D. None of 

these resources would be expected to occur in the rock 

types present in the study areas.

Conclusions for the Western Otay Mountain 

Wilderness Study Area

The northwestern part of the Western Otay Mountain 

Wilderness Study Area may have undiscovered gold and 

lead resources. Heavy-mineral concentrations from two 

locations in this part of the study area contained detectable 

gold and high anomalous lead values. Galena and (or) 

anglesite were also noted in the concentrates collected at 

one of these sites. Although no lead deposits are known 

within either of the two study areas, the Cedar Creek 

deposit (fig. 2), which contains galena with sphalerite, 

native silver (or silver-bearing galena), and other minerals 

sparsely distributed in quartz veins (Weber, 1963, p. 173), 

lies less than 1 mi east of the northeast boundary of the 

Western Otay Mountain Wilderness Study Area. Three 

prospects are located in the southern part of the study area, 

north and west of the Otay Mountain Truck Trail in the 

O'Neal Canyon drainage. Rock samples from these 

prospects contained no significant metallic or nonmetallic 

values. The northwestern part of the Western Otay 

Mountain Wilderness Study Area is considered to have low 

potential, certainty level B, for gold and lead resources. No 

other mineral resources are indicated. There is no potential 

for oil, gas, coal, or geothermal resources in the study area, 

certainty level D. None of these resources would be 

expected to occur in the rock types present in the study 

area.

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Mineral Resources of the Southern Otay Mountain and Western Otay Mountain Wilderness Study Areas, California E13
Pinckney, C.J., Streiff, Daryl, and Artim, E.R., 1979, The 

influence of bedding-plane faults in sedimentary formations 

on landslide occurrence, western San Diego County, 

California: Bulletin of the Association of Engineering 

Geologists, v. 26, p. 289-300.

Rose, A.W., Hawkes, H.E., and Webb, J.S., 1979, Geochemistry 

in mineral exploration, 2nd edition: London, Academic 

Press, 33 p.

Scheidemann, R.C., and Kuper, H.T., 1979, Stratigraphy and 

lithofacies of the Sweetwater and Rosarito Beach 

Formations, southwestern San Diego County, California, and 

northwestern Baja California, Mexico, in Stuart, C.J., ed., A 

guidebook to Miocene lithofacies and depositional 

environments, coastal southern California and northwestern 

Baja California: Society of Economic Paleontologists and 

Mineralogists, Pacific Section, for Geological Society of 

America 1979 Annual Meeting, San Diego, Calif., Nov. 

1979, Guidebook for Field Trips, no. 23, p. 107-118.

Storms, W.H., 1893, San Diego County: California State Mining 

Bureau, Report of the State Mineralogist, v. 11, p. 376-393.

Strand, R.G., compiler, 1962, Geologic map of California, San 

Diego-El Centre sheet: California Division of Mines and

Geology, scale 1:250,000. 

Thompson, C.E., Nakagawa, H.M., and Van Sickle, G.H., 1968,

Rapid analysis for gold in geologic materials, in Geological

Survey research 1968: U.S. Geological Survey Professional

Paper 600-B, p. B130-B132. 

Todd, V.R., Erskine, E.G., and Morton, D.M., in press,

Metamorphic and tectonic evolution of the northern

Peninsular Ranges batholith, southern California, in W.G.

Ernst, ed., Metamorphism and crustal evolution of western

U.S., Rubey Vol. VH: Englewood Cliffs, N. 1, PrenticeHall. 

Tucker, W.B., 1925, San Diego County: California State Mining

Bureau, Mining in California, v. 21, no. 3, p. 325-382. 

Tucker, W.B., and Reed, C.H., 1939, Mineral resources of San

Diego: California Journal of Mines and Geology, v. 35, no.

1, p. 8-55. 

U.S. Bureau of Mines and U.S. Geological Survey, 1980,

Principles of a resource/reserve classification for minerals:

U.S. Geological Survey Circular 831, 5 p. 

Weber, F.H., Jr., 1963, Geology and mineral resources of San

Diego County, California: California Division of Mines and

Geology County Report 3, 309 p.

E14 Mineral Resources of Wilderness Study Areas Southern California and California Desert Conservation Area
APPENDIXES
DEFINITION OF LEVELS OF MINERAL RESOURCE POTENTIAL 

AND CERTAINTY OF ASSESSMENT

LEVELS OF RESOURCE POTENTIAL

H HIGH mineral resource potential is assigned to areas where geologic, geochemical, and geophysical characteristics indicate a geologic environment favorable for resource occurrence, where interpretations of data 

indicate a high degree of likelihood for resource accumulation, where data support mineral-deposit models 

indicating presence of resources, and where evidence indicates that mineral concentration has taken place. 

Assignment of high resource potential to an area requires some positive knowledge that mineral-forming processes 

have been active in at least part of the area.

M MODERATE mineral resource potential is assigned to areas where geologic, geochemical, and geophysical 

characteristics indicate a geologic environment favorable for resource occurrence, where interpretations of data 

indicate reasonable likelihood for resource accumulation, and (or) where an application of mineral-deposit models 

indicates favorable ground for the specified type(s) of deposits.

L LOW mineral resource potential is assigned to areas where geologic, geochemical, and geophysical characteristics 

define a geologic environment in which the existence of resources is permissive. This broad category embraces 

areas with dispersed but insignificantly mineralized rock, as well as areas with little or no indication of having 

been mineralized.

N NO mineral resource potential is a category reserved for a specific type of resource in a well-defined area.

U UNKNOWN mineral resource potential is assigned to areas where information is inadequate to assign a low, 

moderate, or high level of resource potential.

LEVELS OF CERTAINTY

A Available information is not adequate for determination of the level of mineral resource potential.

B Available information only suggests the level of mineral resource potential.

C Available information gives a good indication of the level of mineral resource potential.

D Available information clearly defines the level of mineral resource potential.

Z

LU

o

0-

LU 

U

C£

Oen

LU

C£

LL.

O

A

U/A

UNKNOWN POTENTIAL

B

H/B

HIGH POTENTIAL

M/B

MODERATE POTENTIAL

L/B

LOW POTENTIAL

C

H/C

HIGH POTENTIAL

M/C

MODERATE POTENTIAL

L/C

LOW POTENTIAL

D

H/D

HIGH POTENTIAL

M/D

MODERATE POTENTIAL

L/D

LOW POTENTIAL

N/D

NO POTENTIAL

LEVEL OF CERTAINTY

Abstracted with minor modifications from:

Taylor, R.B., and Steven, T.A., 1983, Definition of mineral resource potential: Economic Geology, v. 78, no. 6, p. 1268-1270.

Taylor, R.B., Stoneman, R.J., and Marsh, S.P., 1984, An assessment of the mineral resource potential of the San Isabel National Forest, south-central Colorado: U.S.

Geological Survey Bulletin 1638, p. 40-42. 

Goudarzi, G.H., compiler, 1984, Guide to preparation of mineral survey reports on public lands: U.S. Geological Survey Open-File Report 84-0787, p. 7, 8.

E16 Mineral Resources of Wilderness Study Areas Southern California and California Desert Conservation Area
RESOURCE/RESERVE CLASSIFICATION

ECONOMIC

MARGINALLY 

ECONOMIC

SUBECONOMIC

IDENTIFIED RESOURCES

Demonstrated

Measured

Rese

Indicated

;rves

I 

Marginal 

Reserves

Demonstrated 

Subeconomic

Resources

i

Inferred

Inferred 

Reserves

Inferred 

Marginal 

Reserves

Inferred 

Subeconomic 

Resources

UNDISCOVERED RESOURCES

Probability Range

Hypothetical Speculative

_

Major elements of m ineral resource classification, excluding reserve base and inferred reserve base. Modified from McKelvey, V.E., 1972, Mineral 

resource estimates and public policy: American Scientist, v. 60, p. 32-40; and U.S. Bureau of Mines and U.S. Geological Survey, 1980, Principles 

of a resource/reserve classification for minerals: U.S. Geological Survey Circular 831, p. 5.

Mineral Resources of the Southern Otay Mountain and Western Otay Mountain Wilderness Study Areas, California E17
GEOLOGIC TIME CHART

Terms and boundary ages used by the U.S. Geological Survey in this report

1 

EON

Phanerozoic

Proterozoic

Archean

ERA

Cenozoic

Mesozoic

Paleozoic

Late Proterozoic

Middle Proterozoic

Early Proterozoic

Late Archean

Middle Archean

Early Archean

PERIOD

Quaternary

Neogene 

Subperiod

Tertiary _ . 

Paleogene

Subperiod

Cretaceous

Jurassic

Triassic

Permian

Pennsylvanian 

Carboniferous

Mississippian

Devonian

Silurian

Ordovician

Cambrian

tiRnr\?\

EPOCH

Holocene

Pleistocene

Pliocene

Miocene

Oligocene

Eocene

Paleocene

Late 

Early

Late 

Middle 

Early

Late 

Middle 

Early

Late 

Early

Late 

Middle 

Early

Late 

Early

Late 

Middle 

Early

Late 

Middle 

Early

Late 

Middle 

Early

Late 

Middle 

Early

pre-Archean2

AGE ESTIMATES OF 

BOUNDARIES (in Ma)

 0.010

 1.7

 5

T A

1Q

 55

 66

96

1 1Q

 205

 -240

 290 

-330

...... _ icj\

 410

 500

 1600 

 2500

 3400

 Azcn 

'Rocks older than 570 Ma also called Precambrian, a time term without specific rank, 

informal time term without specific rank.

E18 Mineral Resources of Wilderness Study Areas Southern California and California Desert Conservation Area
Mineral Resources of 

Wilderness Study Areas: 

Southern California and 

California Desert Conservation Area

This volume was published as chapters A E

U.S. GEOLOGICAL SURVEY BULLETIN 1711
DEPARTMENT OF THE INTERIOR 

DONALD PAUL MODEL, Secretary

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director
CONTENTS

[Letters designate the separately published chapters]

(A) Mineral Resources of the Indian Pass and Picacho Peak Wilderness Study Areas, 

Imperial County, California, by David B. Smith, Byron R. Berger, Richard M. 

Tosdal, David R. Sherrod, Gary L. Raines, Andrew Griscom, Maryann G. Helferty, 

Clayton M. Rumsey, and Arel B. McMahan.

(B) Mineral Resources of the Sawtooth Mountains and Carrizo Gorge/Eastern McCain 

Valley Wilderness Study Areas, San Diego County, California, by Victoria R. Todd, 

James E. Kilburn, David E. Detra, Andrew Griscom, Daniel H. Knepper, Jr., Fred A. 

Kruse, Eric Gather, and David A. Lipton.

(C) Mineral Resources of the Fish Creek Mountains Wilderness Study Area, Imperial 

County, California, by Victoria R. Todd, David E. Detra, James E. Kilburn, Andrew 

Griscom, Fred A. Kruse, and Harry W. Campbell.

(D) Mineral Resources of the Jacumba (In-ko-pah) Wilderness Study Area, Imperial 

County, California, by Victoria R. Todd, James E. Kilburn, David E. Detra, Andrew 

Griscom, Fred A. Kruse, and Edward L. McHugh.

(E) Mineral Resources of the Southern Otay Mountain and Western Otay Mountain 

Wilderness Study Areas, San Diego County, California, by Victoria R. Todd, 

Gregory K. Lee, Howard W. Oliver, J. Douglas Causey, and Steven W. Schmauch.
GPO 585-045/78057
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