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Mount Tamalpais, Marin Co., California, USA

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Latitude & Longitude (WGS84): 37° 55' 39'' North , 122° 35' 26'' West
Latitude & Longitude (decimal): 37.92750,-122.59083
Köppen climate type:Csb : Warm-summer Mediterranean climate

A summit located in Marin County. A public road leads to the summit where there is car park and viewing area. The summit provides a spectacular view of the entire northern San Francisco Bay area, including the city and the Golden Gate bridge.

Mineral List

Mineral list contains entries from the region specified including sub-localities

2 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: 2991649
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]

145 - 201.3 Ma

ID: 2711512
Franciscan Complex

Age: Jurassic (145 - 201.3 Ma)

Stratigraphic Name: Franciscan Complex

Description: Mélange: A tectonic mixture of variably sheared shale and sandstone containing (1) hard tectonic inclusions largely of greenstone, chert, graywacke, and their metamorphosed equivalents, plus exotic high-grade metamorphic rocks and serpentinite and (2) variably resistant masses of graywacke, greenstone, and serpentinite up to several miles in longest dimension, and including minor discrete masses of limestone too small to be shown. Blocks and resistant masses have survived the extensive shearing evident in the mélanges matrix, and range in abundance from less than 1 to 50 percent or more of the rock mass. The degree of shearing in the unit ranges from gouge to unsheared rock, with resistant masses relatively unsheared and matrix sheared. Severely sheared shale is abundant in areas where blocks are abundant. Fresh, relatively unsheared rock is hard, the larger resistant masses are pervasively fractured, and blocks are commonly tough and relatively unfractured. Sandstone is graywacke, grayish green where fresh, weathering to brown, commonly medium to coarse grained, containing abundant angular lithic grains and no detrital potassium feldspar, except rarely as much as 5 percent. Graywacke is locally veined with quartz and carbonate, and usually contains microscopic secondary pumpellyite. Topography of coherent masses resembles that of unit Kfs, whereas highly sheared matrix typically yields subdued, gently-rounded topography. Good exposures of both sheared matrix and relatively unsheared graywacke and shale occur at the crushed rock quarry just east of the intersection of State Highway 17 and U.S. Highway 101, in Greenbrae (Novato quadrangle)

Reference: Blake, M.C. Jr., R.W. Graymer, and D.L. Jones. Geologic map and map database of parts of Marin, San Francisco, Alameda, Contra Costa, and Sonoma Counties, California. U.S. Geological Survey Miscellaneous Field Studies MF 2337. [38]

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

Localities in this Region


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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Murdoch, Joseph & Robert W. Webb (1966), Minerals of California, Centennial Volume (1866-1966): California Division Mines & Geology Bulletin 189: 311.

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