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Black Mountain Mine (Black Mountain group), Black Mountain, Poway, San Diego Co., California, USA

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Latitude & Longitude (WGS84): 32° 58' 59'' North , 117° 6' 50'' West
Latitude & Longitude (decimal): 32.9830555556, -117.113888889

A former As-Au mine located in sec. 5, T14S, R2W, SBM, 1.0 km (3,400 feet) NNE of Black Mountain (coordinates of record), on its N slope, and 7.6 km (4.7 miles) WNW of Poway, on state park land. Note the property is located within the Black Mountain Open Space Park and is closed to collecting. Alternate coordinates provided: 32°59'24"N, 117°06'40"W

According to 2009 article in the San Diego Union Tribune, "in the 1920s, there was a short-lived boom in white arsenic because it was an ingredient in a pesticide that attacked boll weevils, which were infesting Southern cotton crops. Frank Hopkins, an Escondido rancher, rodeo cowboy and actor, used his Hollywood contacts to fund an arsenic mine on the north slope of Black Mountain. Several years of cold winters and dry summers in the South effectively eliminated the boll weevils, so demand for white arsenic fell. The mine was abandoned in 1927, but its concrete dust chamber, shafts and oven remain."[1]

However according to a contemporaneous article, Mr. Hopkins and his partners may also have had interest in another mineral at this site - gold. According to a 1939 article, "known to be conservative" J.N. McLeod "a nationally known mining engineer", "obtained 150 samples from test holes and reports they assayed from $13.60 a ton at the extreme south end of the workings to $113 at the north end."[2] In 1939, the US Official gold price was set at $35 per troy ounce.

In 1926, the 180-foot-long concrete stack was constructed for processing the arsenic. The arsenic was mined, crushed, and heated to a vaporizing temperature. The condensed arsenic vapor was collected from the baffles inside the stack.[3] Downhill of the stack, is the mine's oven, a few collection bins (perhaps for cyanide leaching?) and collapsed outbuildings.

To the west of the oven and in front of what seems to be a collapsed mine adit, is a small pile of arsenopyrite ore, some with small, unremarkable pyrite crystals. Getting to the location also requires off trail bush-wacking, another activity frowned on by the park rangers, as dangers at this site include bees, ticks, thorns, mountain lions (2011 sightings), snakes, heat exhaustion and unstable structures.[4] And as readers of this website likely already know, elemental arsenic and arsenic compounds are classified as “toxic” and “dangerous for the environment” in the European Union under directive 67/548/EEC.

The Park is located in the geological area known as the “Poway Quadrant” which consists of rock units called “Santiago Peak Volcanics.” The Santiago Peak Volcanics comprise an elongate belt of mildly metamorphosed volcanic, volcaniclastic, and sedimentary rocks that crop out from the southern edge of Los Angeles Basin southward towards Mexico (California Division of Mines, 1975).

Local rocks include Mesozoic volcanic rocks, unit 4 (Peninsular Ranges) (per MRDS database).

Mineral List

1 valid mineral.

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.


Tucker, W. Burling (1925), San Diego, Ventura Counties: California Mining Bureau. Report 21: 329.

Weber, F.H., Jr. (1963a) Mines and mineral resources of San Diego County, California. California Division of Mines and Geology County Report 3, 309 pp.: 49.

Murdoch, Joseph & Robert W. Webb (1966), Minerals of California, Centennial Volume (1866-1966): California Division Mines & Geology Bulletin 189: 87.

Pemberton, H. Earl (1983), Minerals of California; Van Nostrand Reinholt Press: 77.

USGS (2005), Mineral Resources Data System (MRDS): U.S. Geological Survey, Reston, Virginia, loc. file ID #10262361.

U.S. Bureau of Mines, Minerals Availability System (MAS) file ID #0060730632.

External Links - [1] "Black Mountain's Miner's Ridge Loop Trail offers an abundance of colors", The San Diego Union Tribune, May 28, 2009 - [2] "Gold Strike near Lake Hodges", The Vista Press, March 2, 1939 - [3] Abandoned San Diego website

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