California State Gem Mine (Dallas Gem Mine; Benitoite Mine; Benitoite Gem Mine; Gem Mine), Santa Rita Peak, New Idria District, Diablo Range, San Benito Co., California, USA
|Latitude & Longitude (WGS84):||36° 20' 9'' North , 120° 36' 19'' West|
|Latitude & Longitude (decimal):||36.33611,-120.60528|
|Köppen climate type:||Csb : Warm-summer Mediterranean climate|
A former gemstone and specimen occurrence/mine located in the SW¼NE¼ sec. 25, T18S, R12E, MDM, 1.2 km (0.8 miles; 4,000 feet) SSW of Santa Rita Peak (coordinates of record), at the headwaters of the San Benito River, on formerly private (patented) land, now turned over to the state of California. MRDS database stated accuracy for this location is 100 meters.
Mineralization is a gemstone deposit. The deposit is comprised of natrolite veins cutting a glaucophane schist inclusion in a serpentinite body. Local rocks include ultramafic rocks, chiefly Mesozoic, unit 3 (Coast Ranges and Western Klamath Mountains).
Note: The majority of specimens from this locality have been prepared by dissolving away the enclosing natrolite with hydrochloric acid.
Workings include unspecified underground openings (the topo map reflects a large shaded area of mining activity with 1 adit symbol labeled "gem mine" at this point).
Commodity ListThis is a list of exploitable or exploited mineral commodities recorded at this locality.
31 valid minerals. 6 (TL) - type locality of valid minerals.
Rock Types Recorded
Select Rock List TypeAlphabetical List Tree Diagram
Entries shown in red are rocks recorded for this region.
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 Macrostrat.org
66 - 145 Ma
|Mesozoic sedimentary rocks|
Age: Cretaceous (66 - 145 Ma)
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. 
|Late Jurassic - Middle Jurassic|
145 - 174.1 Ma
|Ultramafic rocks, chiefly Mesozoic, unit 3 (Coast Ranges and Western Klamath Mountains)|
Age: Jurassic (145 - 174.1 Ma)
Stratigraphic Name: Josephine Peridotite
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.