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( BEHRMAN, 1

978)

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MELONES

F AULT

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MOUNT A

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120°52'30”38°22'30”

38°15'120°52'30”

38°15'120°45’

120°45’38°22'30”

STATE OF CALIFORNIA – GAVIN NEWSOM, GOVERNORTHE NATURAL RESOURCES AGENCY – WADE CROWFOOT, SECRETARY

DEPARTMENT OF CONSERVATION – DAVID BUNN, DIRECTOR CALIFORNIA GEOLOGICAL SURVEYWILLIAM R. SHORT, ACTING STATE GEOLOGIST

This geologic map was funded in part by the USGS National Cooperative Geologic MappingProgram, Statemap Award no. G18AC00193

PRELIMINARY GEOLOGIC MAP OF THE JACKSON 7.5' QUADRANGLEAMADOR AND CALAVERAS COUNTIES, CALIFORNIA

VERSION 1.0By

Peter J. Holland and Matt D. O’NealDigital Preparation

byPeter J. Holland, Carlos I. Gutierrez, and Janine E. Bird

2019

PRELIMINARY GEOLOGIC MAP OF THE JACKSON 7.5’ QUADRANGLE, CALIFORNIA

Copyright © 2019 by the California Department of ConservationCalifornia Geological Survey. All rights reserved. No part ofthis publication may be reproduced without written consent of theCalifornia Geological Survey.

"The Department of Conservation makes no warranties as to thesuitability of this product for any given purpose."

Coordinate System:Universal Transverse Mercator, Zone 10NNorth American Datum 1927

Topographic base from U.S. Geological SurveyJackson 7.5-minute Quadrangle, 1962, photoinspected 1973. Shaded relief image derived from USGS 1/3 arc-second National Elevation Dataset (NED).

Preliminary Geologic Map available from:https://www.conservation.ca.gov/cgs/maps-data/rgm/preliminary

Professional Licenses and Certifications: P. Holland - PG No. 7994, CEG No. 2400

CaliforniaDepartment of ConservationCal i forn ia Geologica l Sur vey

13.3 °

MA

GN

ETI

C N

OR

TH

TRU

E N

OR

TH

Approximate MeanDeclination, 2019

Scale 1:24,000

Contour Interval 20 FeetNational Geodetic Vertical Datum of 1929

7000 FEET1000 10000 2000 3000 4000 5000 6000

.5 1 KILOMETER1 0

1/ 21 0 1 MILE

SELECTED REFERENCES

Bartow, J.A., and Marchand, D.E., 1979, Preliminary geologic map of the Cenozoic deposits of the Sutter Creek quadrangle, California (scale 1:62,500): U.S.G.S. Open-File Report 79-436.

Behrman, P.G., 1978, Pre-Callovian Rocks, West of the Melones Fault Zone, Central Sierra Nevada Foothills: in Howell, D.G., and McDougall, K.A., eds, Mesozoic Paleogeography of the Western United States, Pacific Coast Paleogeography Symposium 2, SEPM, p 337-348.

Behrman, P.G., and Parkison, G.A., 1978, Paleogeographic Significance of the Callovian to Kimmeridgian Strata Central Sierra Nevada Foothills, California: in Howell, D.G., and McDougall, K.A., eds, Mesozoic Paleogeography of the Western United States, Pacific Coast Paleogeography Symposium 2, SEPM, p 349-360.

California State Mining Bureau, 1906, The Structural and Industrial Materials of California; Bulletin No. 38, 412 p.

Clark, L.D., 1964, Stratigraphy and Structure of the Western Sierra Nevada Metamorphic Belt, California: U.S. Geological Survey Professional Paper 410, 70 p.

Creely, S. and Force, E.R., 2007, Type Region of the Ione Formation (Eocene), Central California: Stratigraphy, Paleogeography, and Relation to Auriferous Gravels; U.S. Geological Survey Open File Report 2006-1378, 65 p.

Duffield, W.A. and Sharp, R.V., 1975, Geology of the Sierra Foothills Mélange and Adjacent Areas, Amador County, California: U.S. Geological Survey Professional Paper 827, 30 p.

HCG, 1997, Engineering Geologic Map, Pardee Reservoir Enlargement Project: Pardee Project Team. Unpublished East Bay MUD map.

Knopf, A., 1929, The Mother Lode system of California: U.S.G.S. Professional Paper 157, 88p.

Logan, C.A., 1934, Mother Lode Gold Belt of California. C.D.M.G. Bulletin 108, 221 p.

Loyd R.C., 1983, Mineral Land Classification of the Sutter Creek 15’ Quadrangle, Amador and Calaveras Counties, California: C.D.M.G. Open-File Report 83-36, 42 p.

Miller, J., 1982, Stratigraphy, structure, and metamorphism of the Calaveras Complex in part of Amador and Calaveras Counties, California: University of California, Santa Cruz, unpublished M.S. thesis.

Schweickert, R.A., 2015, Jurassic evolution of the Western Sierra Nevada metamorphic province, in Geological Society of America Special Paper 513, p. 299-358.

Taliaferro, N.L., 1943, Manganese deposits of the Sierra Nevada, their genesis and metamorphism: California Division of Mines Bulletin 125, p. 277-332.

Taliaferro, N.L., 1950, Geologic map of the Sutter Creek quadrangle, University of California, Berkeley, unpublished, scale 1:62,500.

Turner, H.W., 1894, Jackson Peak folio, California: U.S. Geological Survey Geologic Atlas of the United States Folio GF-11, scale 1:125,000.

U.S. Army Corps of Engineers, 1995, Geologic and seismologic investigation, New Hogan dam and reservoir, Calaveras County, California.

CORRELATION OF MAP UNITS

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Pliocene

Holocene

Pleistocene

Miocene

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Oligocene

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West Point

$ 0 105 Miles

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(PLACERVILLE 30’×60’)

(OAKDALE 30’×60’)

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Amador Co.

Stanislaus Co.

San Joaquin Co.

Current Year - FY 2018-2019

STATEMAP geologic mapping projectswithin the San Andreas 30’×60’ quadrangle

Previously completed projects

Other Mapping

IRISH

HILL

IONE

JACKSON

VALLEY

SPRINGS

JENNY

LIND

SAN

ANDREAS

WALLACE

VALLEY

SPRINGS

SWANGELS

CAMP

25

MAP SYMBOLS

?

? Contact between map units – Solid where accurately located; short dash where inferred; long dash where approximately located; queried where identity or existence is uncertain

Fault – Solid where accurately located; long dash where approximately located; short dash where inferred; dotted where concealed; queried where identity or existence is uncertain. Arrow and number indicate direction and angle of dip of fault plane

Strike and dip of sedimentary beds:

Inclined bedding; number indicates dip angle in degrees

Vertical bedding

Strike and dip of metamorphic foliation:

Inclined foliation; number indicates dip angle in degrees

Vertical foliaiton

Landslide – Arrows indicate principal direction of movement

25

27

SURFICIAL UNITS

Artificial fill (historic)—Consists of man-made deposits of earth materials that may be engineered or non-engineered. Mostly includes highway and railroad embankments as well as dams and large building pads.

Tailings (historic)—Consists of man-made deposits of earth materials that are the by-product of mining processes.

Alluvium (Holocene to Pleistocene)—Alluvium deposited in fan, terrace or fluvial environments. Typically consists of poorly to moderately sorted sand, silt and gravel. It’s noted in the Jackson quadrangle that clay rich alluvium occurs in areas of serpentinite bedrock.

Alluvial fan deposits (Holocene to Pleistocene)—Unconsolidated deposits of various clast size generally toward the base of local areas of relatively high relief. Mostly mapped by lidar in the Calaveras County portion of the map with limited field observations. Also mapped north of Jackson. Locally these areas contain debris fan lobes and may be as young as late Holocene but in many places, they appear to be dissected by erosion and may be of Pleistocene age.

Landslide deposits (Holocene to Pleistocene)—Mostly unconsolidated deposits of various composition and depth. Most landslides are mapped in the Calaveras County portion of the map, given the availability of 1m lidar coverage at time of mapping. More landslides are likely present in Amador County portion of map but were not easily identified on satellite and/or aerial photo imagery. Includes, talus slope on west and south flank of Waters Peak comprised of blocky bouldery debris of Ione formation sandstone. Some blocks are up to 10 meters in diameter. Other blocks appear to have rolled down to base of hill.

Older alluvium (early Holocene to Pleistocene)—Unconsolidated fluvial deposits that are adjacent to streams but appear to be disconnected from modern deposition. Mapped by lidar in the Calaveras County portion of the map.

TERTIARY UNITS

Mehrten Formation (early Pliocene to Miocene)—Conglomerate and interbedded sandstone. Compositionally distinct – dominated by andesitic clasts, often well rounded porphyritic cobbles. Sandstones are often dark gray with an abundance of volcanic grains. Andesitic boulders up to approximately 0.6 meters in diameter occasionally occur along the base. Includes intraformational boulder conglomerates exposed in railroad cuts along the Amador Central Railroad. The volcanic lahar deposits that occur in the Mehrten in adjacent quadrangles are mostly absent in the Jackson Quadrangle. A thin layer of Valley Springs may be present below the Mehrten Formation at John Bull Peak as there is an unmappable source of siliceous cobbles observed in that area mostly as float.

Ione Formation (middle Eocene)—Sandstone and conglomerate. The exposures on the eastern portion of the quadrangle are mostly conglomerate with predominantly well rounded siliceous gravel and cobble clasts. The exposures on Waters Peak are predominantly moderately cemented, fine to coarse grained, quartz rich sandstone. There are well rounded quartzite cobbles and gravel towards the base of these exposures. Creely and Force (2007) refer to the Ione formation exposed on Waters Peak as the “hard white sandstone” of the upper Ione marine facies. They note that the Waters Peak exposures have sand sized detrital kaolinite grains. The Ione also occurs in an area ½ mile south of Waters Peak historically known as O’Neal Quarry (California State Mining Bureau, 1906). The sandstone there was quarried and used for building stone in the late 1890’s. It is currently poorly exposed with mostly exposures of angular quartz ferricrete observed. It’s noted that there is an approximately 75 meters vertical offset from the Ione Formation exposed at Waters Peak and the Ione at O’Neal Quarry.

MESOZOIC AND PALEOZOIC UNITS

Dioritic intrusive rocks (Cretaceous to Jurassic)—Small plutonic bodies of diorite and some gabbro. Green, fine- to coarse-grained. May include some more felsic and more mafic rocks.

Copper Hill Volcanics (Late Jurassic)—Undifferentiated meta-andesite, meta-basalt, meta-rhyolite, meta-tuff, meta-breccia, meta-conglomerate, meta-sandstone with minor amounts of slate, felsite and serpentinite. Generally dark to medium green with varying degrees of schistose texture. Volcanic rocks are often porphyritic with plagioclase the most common phenocrysts. Named by Clark (1964) with the type section on the Cosumnes River in Amador and El Dorado Counties north of the quadrangle. Subdivided into the following units:

Quartz porphyry—Light gray to light yellow brown quartz porphyry. Appears to be an intrusive unit that may have formed in fault zones. In some instances, the surrounding slate and more mafic volcanic rocks occur as breccia fragments encased within the quartz porphyry. Often includes rhyolitic and felsitic rocks. Quartz phenocrysts are often euhedral and up to 1 cm in diameter. Many small prospects and pits have been excavated into this unit.

Conglomerate—Conglomerate unit in which the clasts are generally heterogenous. Includes sandstone interbeds. Graded turbidite beds (younging to the east) were observed where this unit is exposed southwest of Copper Mine Gulch

Tuff—Tuff sequence with pumice lapilli. Includes some tuff breccia.

Rhyolite—Rhyolite occurrence mapped separately in northwestern portion of the quadrangle. Includes quartz phenocrysts and probable relict flow banding.

Feldspar porphyry—Plagioclase and augite porphyry. Plagioclase is often more abundant than augite. Occasionally, augite phenocrysts are absent and are at times more abundant than plagioclase. Often brecciated and appears to have been deposited as a flow breccia or auto breccia. Can be massive with no apparent bedding and faint to absent foliation. The most prominent and rugged outcrops of Copper Hill are predominantly made of this unit.

Salt Spring Slate (Late Jurassic)—Black sericite slate is the dominant lithology but also includes greywacke, tuff, and conglomerate. Late Oxfordian to early Kimmeridgian fossils have been collected in this formation along the Cosumnes River (Clark, 1964).

Gopher Ridge Volcanics (Late Jurassic)—Includes breccia, lithic and vitric tuffs, and massive flow rocks, locally exhibiting pillow structure. Compositions range from mafic to intermediate. Named by Clark (1964) for exposures along the Calaveras River within the Valley Springs quadrangle to the south. Locally divided into:

Quartz porphyry—Light gray to light yellow brown quartz porphyry exposed in southwest corner of quadrangle.

DESCRIPTION OF MAP UNITS

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Mariposa Formation (Late Jurassic)—Slate, tuff, and greywacke. Includes intervals of greenstone not shown on map around Jackson.

Brower Creek member—Mostly coarse breccia with lesser amount of fine tuff. Named by Clark (1964) and difficult to distinguish from underlying Goat Hill member of the Logtown Ridge formation (Parkison, 1976).

Quartz ankerite vein—Massive quatz vein east of Kennedy Mine and exposed at Jackson Gate. Predominantly light-brown to yellow with subordinate ankerite.

Logtown Ridge Formation (Middle to Late Jurassic)—Metamorphosed pyroclastic deposits, basaltic to andesitic lava, and associated breccia. Named by Taliaferro (1943) and divided into mappable members by Duffield and Sharp (1975).

Pokerville member—Augite porphyry greenstone flows with local pillow structures, breccia, and minor bedded tuffaceous greenstone.

Goat Hill member—Thinly- to thickly-bedded very fine to medium grained tuff, coarse pumice lapilli tuff in graded beds and thickly-bedded fine to coarse volcanic breccia that grades upward into medium-fine grained tuff. Conformably overlies the Rabbit Flat member. The age of the Goat Hill Member is well established ass Callovian to late Jurassic by the occurrence of the ammonite Pseudocadoceras (Duffield and Sharp, 1975). Parkison (1976) notes that in the southern part of the quadrangle it is difficult to distinguish with the overlying Brower Creek member of the Mariposa Formation.

Rabbit Flat member—Coarsely porphyritic augite andesite-basalt breccia and massive flows or sills, as well as minor bedded pyroclastic rocks. Breccia is typically medium bluish-green in outcrop and contains abundant dark euhedral augite phenocrysts between 2 and 5 mm. The base is in fault contact with mélange to the west. Clasts typically between 2 and 5 cm and are often ellipsoidal or disc shaped. Named by Duffield and Sharp (1975) and mapped north of Mokelumne River. Mapped by Parkison (1976) south of Mokelumne River.

Mélange Belt (Mesozoic to Paleozoic)—First recognized by Duffield and Sharp (1975) as a mélange. Previously mapped as the Calaveras Formation in the Jackson quadrangle by Turner (1894) and later included Cosumnes formation of the Amador Group by Taliaferro (1943).

Serpentinite (Jurassic)—Black to bluish gray, sheared to blocky, often with well-developed slaty cleavage. Occasionally contains unserpentinized ultramafic rocks. North of Sunnybrook contains blocks of mostly volcanic rock between 10 and 100m in diameter. Near Chrome Mountain, John Bull Peak and Sunnybrook the serpentinite often is silicified and resembles chert in outcrop.

Predominantly volcanic breccia and with some interbedded tuff. Occasional interbedded shale and greywacke.

Predominantly massive augite and/or plagioclase porphyry volcanic breccia with some tuff, shale and greywacke. Approximately equivalent to Duffield and Sharp’s (1975) ‘Jp’ and ‘Jhi’ units and Parkison’s ‘vb’ unit.

Predominantly massive ash tuff to lapilli tuff with interbedded shale and greywacke.

Siliceous clast rocks, mostly fine-grained quartzite and chert pebble conglomerate

Siliceous slate and shale light in color, without chert.

Siliceous slate and shale with thinly bedded to massive chert.

Predominantly clay shale with some interbedded greywacke with rare conglomerate. May contain isolated lenses of limestone. Roughly correlative to Duffield and Sharp’s ‘sg’ unit and Parkison’s ‘css’ unit.

Conglomerate with clay shale and greywacke. Roughly correlative to Duffield and Sharp’s (1975) ‘c’ unit and Parikson’s (1976) ‘cssc’ unit.

Limestone, grey, predominantly massive, fine to coarsely-crystalline limestone.

Interbedded clay shale with some interbedded greywacke, fine tuff, volcanic breccia and massive flow rocks (Parkison, 1976).

Diabase, locally gabbroic, both massive and segregated into very thin mafic and felsic layers (Parkison, 1976).

Gabbro—Fine- to medium-grained. The three gabbro bodies south of Highway 88 were mapped by Taliaferro (1950) and were inaccessible during the current mapping. The eastern most of these three bodies was described by Knopf (1929) as quartz diorite.

Massive greenstone and interbedded chert.

Melones Fault Zone rocks

Don Pedro terrain (Jurassic)—Belt of sheared phyllite and metavolcanic schist previously mapped as “metavolcanics and phyllitic rocks” by Miller (1982) and “Rocks within the Melones Fault Zone” by Loyd and Bane (1983). Includes a narrow band of Calaveras Formation that was mapped by Knopf (1929) and Logan (1934) approximately between the Moore Mine and Hunts Gulch. Knopf (1929) also shows a lens of limestone on his map south of the Moore Mine which could not be very verified by our mapping and is not shown here.

Calaveras Complex (Triassic to Paleozoic)—Well foliated phyllite, slate and chert. In thin section, can exhibit well-developed crenulations, which are not always apparent in hand sample.

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