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Mount Diablo Mine (Mt. Diablo Mine; Diablo Mine; Ryne Mine), Mount Diablo (Mt Diablo), Clayton, Diablo Range, Contra Costa Co., California, USA

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Latitude & Longitude (WGS84): 37° 52' 54'' North , 121° 54' 46'' West
Latitude & Longitude (decimal): 37.88167,-121.91278
Köppen climate type:Csb : Warm-summer Mediterranean climate

A former Hg occurrence/mine located in the SE¼ sec. 29, T1N, R1E, MDM, on the upper E side of Mount Diablo (just E of the summit). Discovered in 1863. Operated by the Nevada Scheelite Company (1956). Owned by the Guadelupe Mining Company. The Mount Diablo Mine and the Ryne Mine were consolidated in 1930. Worked 1875-1877 and again briefly in 1930. Last produced in 1953. MRDS database stated accuracy for this location is 100 meters. Native Americans used the cinnabar in tribal ceremonies. Later the deposit was mined as a placer.

Mineralization is along the contact of a diapir (upthrust plug) of Franciscan sediments and serpentine intruded into sedimentary rocks of the Great Valley sequence. The ore body is irregular and tabular and dips N50E at a thickness of 1.83 meters, a width of 60.96 meters and a length of 39.62 meters. Rhyolite plugs occur nearby. Bituminous clays (Black Alta) also occurs. Local alteration included serpentine converted to silica-carbonate rock. Associated rocks include Late Jurassic-Late Cretaceous rhyolite. Local rocks include Franciscan Complex, unit 1 (Coast Ranges).

Workings include surface and underground openings with a length of 1,219.2 meters and an overall depth of 152.4 meters.

Production statistics: Year: 1962 (period = to 1962): Hg (estimated): ^6 pounds/ton (2,711 grams/metric ton).

Low-grade reserves still exist with 17,000 tons of indicated and inferred reserves.

Commodity List

This is a list of exploitable or exploited mineral commodities recorded at this locality.

Mineral List

23 valid minerals. 1 (TL) - type locality of valid minerals.

Rock Types Recorded

Note: this is a very new system on and data is currently VERY limited. Please bear with us while we work towards adding this information!

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Alphabetical List Tree Diagram

Regional Geology

This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.

Click on geological units on the map for more information. Click here to view full-screen map on

Cretaceous - Jurassic
66 - 201.3 Ma

ID: 2943858
Franciscan Complex, unit 1 (Coast Ranges)

Age: Mesozoic (66 - 201.3 Ma)

Stratigraphic Name: Franciscan Complex; Dothan Formation; Honda Formation; San Luis Formation; Valentine Spring Formation

Description: Franciscan complex: Cretaceous and Jurassic sandstone with smaller amounts of shale, chert, limestone, and conglomerate. Includes Franciscan melange, except where separated--see KJfm.

Comments: Coast Ranges. Primarily Yolla Bolly, Central, and San Simeon terranes of Silberling et al. (1987). Consists primarily of variably deformed and metamorphosed graywacke, mudstone, and chert.

Lithology: Major:{sandstone,mudstone}, Minor:{chert}, Incidental:{limestone, conglomerate, greenstone, serpentinite, gabbro, amphibolite, schist, felsic volcanic}

Reference: Horton, J.D., C.A. San Juan, and D.B. Stoeser. The State Geologic Map Compilation (SGMC) geodatabase of the conterminous United States. doi: 10.3133/ds1052. U.S. Geological Survey Data Series 1052. [133]

Late Cretaceous - Jurassic
66 - 201.3 Ma

ID: 2543281
Franciscan Complex

Age: Mesozoic (66 - 201.3 Ma)

Description: basalt and chert

Reference: Graymer, R.W., D.L. Jones, E.E. Brabb. Preliminary geologic map emphasizing bedrock formations in Contra Costa County, California. U.S. Geological Survey Open-File Report 94-622. [86]

Data and map coding provided by, used under Creative Commons Attribution 4.0 License

This page contains all mineral locality references listed on This does not claim to be a complete list. If you know of more minerals from this site, please register so you can add to our database. This locality information is for reference purposes only. You should never attempt to visit any sites listed in without first ensuring that you have the permission of the land and/or mineral rights holders for access and that you are aware of all safety precautions necessary.


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Ransome, Alfred Leslie & J.L. Kellogg (1939) Quicksilver resources of California. California Division Mines Report 35: 377.
Ross, C.P. (1940) Quicksilver deposits of the Mount Diablo region, Contra Costa County, California. USGS Bulletin 922-B, 54 pp.: 41, 42, 44.
Davis, Fenelon Francis & J.W. Vernon (1951) Mines and mineral resources of Contra Costa County, California. California Journal of Mines and Geology: 47(4): 575-576.
Palache, C., Berman, H., and Frondel, C. (1951) The System of Mineralogy of James Dwight Dana and Edward Salisbury Dana, Yale University 1837-1892, Volume II: 492.
California Division of Mines (1952) Mineral Information Service: 5(1) (January, 1952): 2.
Davis, Fenelon Francis and H.B. Goldman (1958) Mines and mineral resources of Contra Costa County. California Journal of Mines and Geology: 54(4): 530-535.
Pampeyan, Earl Haig (1963) Geology and mineral deposits of Mount Diablo, Contra Costa County, California: California Division Mines & Geol., Special Report 80, 31 pp.: 24.
Holmes, Jr., G.W. (1965) Mercury in California: in: U.S. Bureau of Mines Information Circular 8252.
Murdoch, Joseph & Robert W. Webb (1966) Minerals of California, Centennial Volume (1866-1966): California Division Mines & Geology Bulletin 189: 148, 156, 178, 213, 254, 258, 261, 323, 332, 337, 349, 379, 382.
White, D.E. (1967) Mercury and base-metal deposits with associated thermal and mineral waters. In: H.L. Barnes (Editor), Geochemistry of hydrothermal ore deposits. Holt Reinhart and Winston, New York: 585, 591.
Pemberton, H. Earl (1983) Minerals of California; Van Nostrand Reinhold Press: 64, 74, 127, 185, 263, 264, 266, 270, 273, 274, 275, 278, 303, 351, 427.
USGS (2005) Mineral Resources Data System (MRDS): U.S. Geological Survey, Reston, Virginia, loc. file ID #10040642 & 10138061.
U.S. Bureau of Mines Minerals Availability System/Mineral Industry Location System (MAS/MILS): file #0060130026.
Baailey, E.H., USGS, personal files data.

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