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Oat Hill Mines, Aetna Springs, East Mayacmas District, Mayacmas Mts (Mayacamas Mts), Napa Co., California, USA

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Latitude & Longitude (WGS84): 38° 40' 30'' North , 122° 31' 37'' West
Latitude & Longitude (decimal): 38.67500,-122.52694
Köppen climate type:Csb : Warm-summer Mediterranean climate

A former Hg mine complex located in secs. 27, 28, 33 & 34, T10N, R5W, MDM, 4.6 km (2.9 miles) WNW of Aetna Springs.

Mineralization is Hg deposits associated with fault structures and the borders of serpentine masses. Pyrite is always a common accessory mineral.

Workings featured 20 miles of underground tunneling.

Mineral List

9 valid minerals.

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: 2791036
Franciscan melange

Age: Mesozoic (66 - 201.3 Ma)

Stratigraphic Name: Franciscan Complex

Description: Melange of fragmented and sheared Franciscan complex rocks.

Comments: Coast Ranges. Includes areas of Franciscan rocks specifically distinguished as melange on the Geologic Map of California. Includes parts of central and eastern Franciscan belts of Blake et al. (1988)

Lithology: Major:{melange}

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]

Cretaceous - Jurassic
66 - 201.3 Ma

ID: 3190324
Mesozoic tectonic rocks

Age: Mesozoic (66 - 201.3 Ma)

Stratigraphic Name: Franciscan Complex

Comments: metamorphic protolith: mafic volcanics

Lithology: Shale

Reference: Chorlton, L.B. Generalized geology of the world: bedrock domains and major faults in GIS format: a small-scale world geology map with an extended geological attribute database. doi: 10.4095/223767. Geological Survey of Canada, Open File 5529. [154]

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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Becker, George F. (1888b), Becker, George F. (1888b), Geology of the quicksilver deposits of the Pacific slope: USGS Monograph 13, atlas: 354-358.
Fairbanks, Harold W. (1893a), Notes on the geology and mineralogy of portions of Tehama, Colusa, Lake, and Napa Counties: California Mining Bureau. Report 11: 66.
Ross, C.P. (1940b) Quicksilver deposits of the Mayacmas and Sulphur Bank districts, California. USGS Bulletin 922-L: 329-353.
Yates, Robert G. & Lowell S. Hilpert (1946), Quicksilver deposits of eastern Mayacmas district, Lake and Napa Counties, California: California Division of Mines Report 42: 254-268.
Rocks & Minerals (1947): 22: 613.
Davis, Fenelon Francis (1948), Mines and mineral resources of Napa County, California: California Division Mines Report 44: 176-183.
Johnson, Fremont T. & Spangler Ricker (1949), Investigation of Oat Hill mercury mine, Napa County, California: US Bureau Mines Report of Investigation 4542: 491-498.
Dickson, F.W. & G. Tunell (1959), Stability relations of cinnabar and metacinnabar: American Mineralogist: 44: 482-483.
Davis, F.F. and E.H. Bailey (1966) Mercury. California Division Mines and Geol. Bulletin 191: 247-254.
Murdoch, Joseph & Robert W. Webb (1966), Minerals of California, Centennial Volume (1866-1966): California Division Mines & Geology Bulletin 189: 178, 262, 265.
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: 594.
Pemberton, H. Earl (1983), Minerals of California; Van Nostrand Reinholt Press: 111 (map 3-7), 118, 266.

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