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121°0'0''38°15’0”

38°7’30”121°0'0''

38°7’30”120°52’30”

120°52’30”38°15'0"

STATE OF CALIFORNIA – EDMUND G. BROWN JR., GOVERNORTHE NATURAL RESOURCES AGENCY – JOHN LAIRD, SECRETARY

DEPARTMENT OF CONSERVATION – DAVID BUNN, DIRECTOR CALIFORNIA GEOLOGICAL SURVEYJOHN G. PARRISH, Ph.D., STATE GEOLOGIST

PRELIMINARY GEOLOGIC MAP OF THE VALLEY SPRINGS SW 7.5' QUADRANGLE, CALAVERAS, SAN JOAQUIN, AND STANISLAUS COUNTIES, CALIFORNIA

VERSION 1.0By

Carlos I. Gutierrez and Peter J. Holland

Digital Preparation by

Carlos I. Gutierrez

2018

PRELIMINARY GEOLOGIC MAP OF THE VALLEY SPRINGS SW 7.5’ QUADRANGLE, CALIFORNIA

Copyright © 2018 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."

Projection: Universal Transverse Mercator, Zone 10N, North American Datum 1927.

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

Professional Licenses and Certifications: C.I. Gutierrez - PG No. 8686; P. Holland - PG No. 7994, CEG No. 2400

This geologic map was funded in part by the USGS National Cooperative Geologic MappingProgram, Statemap Award no. G17AC00251

Preliminary Geologic Map available from:http://www.conservation.ca.gov/cgs/rghm/rgm/preliminary_geologic_maps.htm

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ValleySprings

Twain Harte

Arnold

Angels Camp

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Bear Valley

Jackson

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SW ANGELS

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Current Year - FY 2017-2018STATEMAP geologic mapping projects

Previously completed projects

Other Mapping

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0 105 Kilometers

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Scale 1:24,000

Contour Interval 40 feetDotted lines represent 20 foot contours

National Geodetic Vertical Datum of 1929

7000 FEET1000 10000 2000 3000 4000 5000 6000

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Approximate MeanDeclination, 2018

SELECTED REFERENCESArkley, R.J, 1962, Soil survey of the Merced area, California: U. S. Department of Agriculture, Soil Survey Series 1950, no 7, 131 p.

Bartow, J.A., 1992, Contact relations of the Ione and Valley Springs Formations in the east-central Great Valley, California: U.S. Geological Survey Open File Report 92-588, Figure 1, scale 1:24,000.

Bartow, J. A.,1994, Tuffaceous ephemeral lake deposits on an alluvial plain, middle Tertiary of central California: Sedimentology, v. 41, p. 215–232, doi:10.1111/j.1365-3091.1994.tb01402.x

Bartow, J.A. and Marchand, D.E., 1979, Preliminary Geologic Map of Cenozoic Deposits of the Valley Springs Quadrangle, California: U.S. Geological Survey Open File Report 79-436, scale 1:62,500.

California Geological Survey, 2009, Smectitic clay deposits - Sierra Nevada Foothills: California Geological Survey Geological GeoHazard Notice 2009-001.

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.

Dewberry, 2013, Calaveras County Lidar Data collected for USGS Contract G10PC00013.

Digital Globe, Inc., 2008, High Resolution Remote Sensing Imagery of Amador, San Joaquin, and Stanislaus Counties.

Gabet, E.J., 2014, Late Cenozoic uplift of the Sierra Nevada, California? A critical analysis of the geomorphic evidence: American Journal of Science, v. 314, p. 1224–1257, doi:10.2475/08.2014.03.

Marchand, D.E. and Allwardt, A., 1981, Late Cenozoic stratigraphic units, northeastern San Joaquin Valley, California: U.S. Geological Survey Bulletin 1470, 70 p.

Marchand, D.E., and Bartow, J.A., 1979, Preliminary geologic map of Cenozoic deposits of the Bellota quadrangle, California: U.S. Geological Survey Open-File Report 79-664, scale 1:62,500.

Marchand, D.E., Bartow, J.A., and Shipley, S., 1981, Preliminary geologic maps showing Cenozoic deposits of the Farmington and Bachelor Valley quadrangles, San Joaquin, Stanislaus and Calaveras counties, California: U.S. Geological Survey Open-File Report 81-1050, scale 1:24,000.

National Agriculture Imagery Program (NAIP) imagery, 2009-2016, US Department of Agriculture.

Piper, A.M. Gale, H.S., Thomas, H.E., and Robinson, T.W., 1939, Geology and ground-water hydrology of the Mokelumne area, California: U.S. Geological Survey Water Supply Paper 780, Report: vii, 230 p., Plate 1, scale 1:63,360.

Tolman, C.F., 1930, A report on the geology of the Mokelumne region: Stanford University, California, 70 p., scale 1:63,360.

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.

Wood, J.L., 2015, personal communication.

Wood, J.L. and Glasmann, J.R., 2013, The nature of early Tertiary soild and sediments - Mineralogy and petrology: Geological Society of America Abstracts with Programs, v. 45, no. 6, p.3.

CORRELATION OF MAP UNITS

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Pliocene

Holocene

Pleistocene

Miocene

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TIAR

Y

Oligocene

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ICM

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Eocene

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MAP SYMBOLS

?

? Contact between map units - Solid where accurately located; long dash where approximately located; short dash where inferred; dotted where concealed; 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.

Strike and dip of sedimentary beds. Number indicates dip angle in degrees

Inclined bedding

Approximate bedding15

40

SURFICIAL UNITS

Artificial fill (historic)—Consists of man-made deposits of earth materials that may be engineered or non-engineered.

Tailings (historic)—Consists of man-made deposits of earth materials generated as a byproduct of mining processes.

Stream channel deposits (Holocene)—Fluvial deposits within, and adjacent to, active stream channels; consists of loose, unconsolidated silt, sand, gravel, and cobbles, with minor clay.

Alluvial deposits, undivided (Holocene to Pleistocene)—Alluvium deposited in fan, terrace, or basin environments. Consists of poorly to moderately sorted sand, silt, and gravel.

Modesto Formation, undivided (early Holocene to late Pleistocene)—Alluvial deposits of arkosic gravel, sand, and silt. Deposited as a series of coalescing alluvial fans extending continuously from the Kern River drainage in the south, to the Sacramento River tributaries in the north. Compositionally, deposits of the Modesto Formation are often indistinguishable from those of the Riverbank, Turlock Lake and Laguna Formations. However, these units are temporally distinct and separated by unconformities. Identity is usually determined by topographic position, geomorphic expression, or (most commonly) by soil development. (Marchand and Allwardt, 1981)

Modesto Formation, upper member—The upper unit has been differentiated from the lower unit on the basis of topographic expression and position, and the presence of a weakly developed buried soil between the lower and upper units (Marchand and Allwardt, 1981).

Modesto Formation, lower member

Riverbank Formation, undivided (Pleistocene)—Consists primarily of arkosic sediment derived mainly from the interior of the Sierra Nevada but also includes locally derived sediment from small drainage basins along the foothills (Marchand and Allwardt, 1981). Marchand and Allwardt (1981) subdivided the Riverbank Formation into three informally designated units on the basis of superposition, paleosols and buried soils, and on geomorphic evidence. The middle unit occurs within the map area:

Riverbank Formation, middle unit

North Merced Gravel (Pleistocene to Pliocene)—Lag gravel deposits typically occuring as a thin veneer of well-rounded cobbles of various types, dependent on local drainage source areas. Tentatively correlated by Bartow and Marchand (1979) to the North Merced Gravel of Arkley (1962).

Laguna Formation (late Pliocene)—Alluvial gravel, sand and silt predominantely of granitic composition. Also contains pebbles and cobbles that are composed dominantly of quartz and metamorphic rock. Sometimes includes andesitic detritus reworked from the Mehrten in the basal portion. Often forms a relatively thin, cobble-rich cap on hills within the quadrangle. It's likely some additional hills in the quadrangle have a thin veneer of the Laguna Formation, although not shown on the map. Soil profile development on weathered surfaces frequently includes a reddish brown duripan horizon cemented by iron oxides, silica, or calcium carbonate Marchand and Allwardt, 1981). The gravels of this unit were thought to be gold-bearing, and where exposed, they are often disturbed by historic strip mining (Marchand and Allwardt, 1981).

TERTIARY SEDIMENTARY AND VOLCANIC UNITS

Mehrten Formation (early Pliocene to Miocene)—Volcanic mudflow deposits interbedded with sandstone and conglomerate. Composition is distinctly dominated by andesite cobbles. Lahar beds laden with andesite cobbles are particularly resistant and often occur as cap rock with corresponding cliff faces.

Valley Springs Formation (Miocene to middle Oligocene)—Tuffaceous sandstone, siltstone, and conglomerate interbedded with tuff and minor clay. Deposits are moderately mature compositionally which reflects the peritropical environment of deposition. The formation may be distinguishable by rhyolitic ash component. Conglomerate is compositionally heterogeneous and features significant proportions of Jurassic metamorphic rocks, quartzite, and chert cobbles. Tuff beds often occur as resistant, cliff-forming outcrops. Green clay rock, which consists of silica-cemented pebbles of expansive smecticic clay, is present near the base of the unit and poses significant geologic hazards related to ground swelling and slope stability (California Geological Survey, 2009; Wood and Glasmann, 2013; Wood, 2015). Petrified wood has been locally reported to occurr in the formation.

Conglomerate—Particularly resistant conglomeratic beds.

Ione Formation (middle Eocene)—Clay, sandstone, and siltstone. Distinctly light in color; dominated by white and light pastel shades of buff, moderately red, and grayish red purple on the weathered surface. Compositionally, this unit is very mature and is distinctly dominated by various forms of quartz, especially vein quartz. Clays are predominantly kaolinitic and are interpreted as having formed in a tropical climate (Wood, 1995). Sandstones are often silica-cemented. Conglomerates typically feature abundant white vein quartz and quartzite cobbles in a matrix of reddish oxidized silt and sand. Finer beds typically feature striking sedimentary structures such as cross-bedding and convolute laminae crossed by more recent subparallel and subvertical joints filled with iron or silica cement. Clays of the Ione Fm. are commercially valuable and have been actively mined for many decades. Early prospectors also suspected the Ione conglomerates of being gold-bearing and where exposed, they are often disturbed by historic exploratory strip mining. The Ione Formation is poorly exposed within the quadrangle.

JURASSIC METAMORPHIC UNITS

Gopher Ridge Volcanics (Late Jurassic)—Includes volcanic breccia, lithic and vitiric tuffs, and massive lavas, locally exibiting pillow structure. Compositions range from mafic to intermediate. Degree of metamorphism varies but schistose textures are common. The Gopher Ridge Volcanics was named by Clark (1964) for exposures along the Calaveras River within the Valley Springs quadrangle. Likely Oxfordian in age (Clark, 1964).

DESCRIPTION OF MAP UNITS

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