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Unnamed Hg occurrence [4], El Corte de Madera Rancho, Portola Valley, San Mateo Co., California, USA

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Latitude & Longitude (WGS84): 37° 21' 27'' North , 122° 12' 26'' West
Latitude & Longitude (decimal): 37.35772,-122.20747
Köppen climate type:Csb : Warm-summer Mediterranean climate

A Hg occurrence located about 3.8 km (2.4 miles) SE of Portola Valley (town), on the Corte de Madera Rancho.

Commodity List

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

Mineral List

4 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

Pleistocene - Miocene
0.0117 - 23.03 Ma

ID: 2939053
Plio-Pleistocene and Pliocene loosely consolidated deposits

Age: Cenozoic (0.0117 - 23.03 Ma)

Stratigraphic Name: Arroyo Seco Gravel; Cache Formation; Carlotta Formation; China Hat Gravel; China Ranch Beds; Coso Formation; Funeral Fanglomerate (part); Furnace Creek Formation; Glen Ellen Formation; Irvington Gravels; Kern River Formation; Laguna Formation; Livermore Gravel; McKittrick Formation; North Merced Gravel; Nova Formation; Packwood Gravels; Paso Robles Formation; Red Bluff Formation; Ricardo Formation; San Benito Gravels; Santa Clara Formation; Saugus Formation; Tehachapi Formation; Tulare Formation; Turlock Lake Formation; Alturas Formation; Anaverde Formation; Canebrake Conglomerate; Chanac Formation; Crowder Formation; Duarte Conglomerate; Esmeralda Formation; Etchegoin Formation; Green Valley Formation; Hathaway Formation; Horned Toad Formation; Hungry Valley Formation; Lockwood Clay; Mecca Formation; Meeke Mine Formation; Mehrten Formation; Morales Formation; Mount Eden Formation; Mulholland Formation; Neroly Formation; Orinda Formation; Oro Loma Formation; Painted Hill Formation; Palm Spring Formation; Panorama Hills Formation; Peace Valley Formation; Petaluma Formation; Potato Sandstone; Purisima Formation; Quatal Formation; Ricardo Formation (part); Ridge Route Formation; Santa Ana Sandstone; San Timoteo Formation; Siesta Formation; Tassajero Formation; Tehama Formation; Tropico Group; Wolfskill Formation

Description: Pliocene and/or Pleistocene sandstone, shale, and gravel deposits; in part Miocene.

Lithology: Major:{sandstone,conglomerate}, Minor:{siltstone,mudstone}, Incidental:{limestone, evaporite, coal, sedimentary breccia}

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]

Early Pleistocene - Late Pliocene
1.806 - 3.6 Ma

ID: 2578200
Santa Clara Formation

Age: Cenozoic (1.806 - 3.6 Ma)

Description: Gray to red-brown poorly indurated conglomerate, sandstone, and mudstone in irregular and lenticular beds. Conglomerate consists mainly of subangular to subrounded cobbles in a sandy matrix but locally includes pebbles and boulders. Cobbles and pebbles are mainly chert, greenstone, and graywacke with some schist, serpentinite, and limestone. On Coal Mine Ridge, south of Portola Valley, conglomerate contains boulders of an older conglomerate as long as one meter. Gray to buff claystone and siltstone beds on Coal Mine Ridge contain carbonized wood fragments as large as 60 cm in diameter. Included in Santa Clara Formation are similar coarse-grained clastic deposits near Burlingame. Sarna-Wojcicki (1976) found a tuff bed in Santa Clara Formation near Woodside, and correlated it with a similar tuff in Merced Formation. Later work indicated that the tuff correlates with the 435 ka Rockland ash (Sarna-Wojcicki, oral comm., 1997). Thickness of Santa Clara Formation is variable but reaches a maximum of about 500 m along Coal Mine Ridge

Reference: Brabb, E.E., R.W. Graymer, D.L. Jones. Geology of the onshore part of San Mateo County, California. U.S. Geological Survey Open-File Report 98-137. [90]

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.


Sort by Year (asc) | by Year (desc) | by Author (A-Z) | by Author (Z-A)
Rogers, Austin Flint (1911a), Eglestonite from San Mateo County, California: American Journal of Science, 4th. Series: 32: 48-50.
Bradley, W.W. (1918), Quicksilver resources of California, with a section on metallurgy and ore dressing: California Mining Bureau. Bulletin 78, 389 pp.: 149.
Davis, Fenelon Francis (1955), Mines and mineral resources of San Mateo County, California: California Journal of Mines and Geology: 51: 401-458.
Murdoch, Joseph & Robert W. Webb (1966), Minerals of California, Centennial Volume (1866-1966): California Division Mines & Geology Bulletin 189: 119, 149, 260.

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