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Picacho District, Chocolate Mts, Imperial Co., California, USA

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Latitude & Longitude (WGS84): 32° 57' 44'' North , 114° 38' 37'' West
Latitude & Longitude (decimal): 32.96231,-114.64369
Other regions containing this locality:Sonoran Desert, North America
Köppen climate type:BWh : Hot deserts climate

Location: The Picacho district is in southeastern Imperial County 20 miles NW of Winterhaven and about 50 miles E of El Centro and 20 miles N of Yuma, Arizona, in the southeastern Chocolate Mountains. The Colorado River is on the north side of the district, and the Chocolate Mountains extend along the southwest margin. The district was named for Picacho Peak, a prominent landmark in the area.

History: Spaniards, developing the nearby Cargo Muchacho and Potholes districts, probably mined the Picacho district as early as 1780. For many years, Mexicans and Indians mined the area by small-scale dry washing methods. Small hand-operated bellows-type washers were employed, or winnowing was done with blankets. Virtually every dry wash in the region was
worked in this fashion, and many small tailings piles from these operations are still visible. Attempts were made to hydraulic the area during the 1890's. The Picacho or Picacho Basin Mine, the largest source of gold in the district, was worked on a large scale from 1904 to 1910. The reported output was $2 million. During this operation the ore was treated in a mill near the Colorado River. The mine was sampled in the 1930's, but there has been only minor prospecting in the district since, and the site of the old town of Picacho on the river was recently made into a state recreation area.

Geology: The central part of the district, which is in a shallow basin, is underlain by interbedded granitic rocks and mica and hornblende schists. A number of diorite dikes may be associated with the gold mineralization. The ridges surrounding the basin and Picacho Peak are composed of andesite, rhyolite, and rhyolite tuff.

Ore Deposits: The ore deposits consist of parallel, thin, gold-bearing stringers in schist. Although the ore bodies at the Picacho Mine contained only a few dollars of gold per ton, several were quite large. The last ore shoot worked at this mine was 250 feet long and 160 feet wide. The placer deposits in the various dry washes usually were shallow and discontinuous. The gold particles were very fine.

A few peridots of good quality have been reported from the gravels of the Picacho region.

Mineral List

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

20 valid minerals.

Rock Types Recorded

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

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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 Macrostrat.org

Miocene - Paleoproterozoic
5.333 - 2500 Ma

ID: 2943761
Precambrian igneous and metamorphic rock complex

Age: to Neogene (5.333 - 2500 Ma)

Description: Complex of Precambrian igneous and metamorphic rocks. Mostly gneiss and schist intruded by igneous rocks; may be Mesozoic in part.

Comments: Present only in southern California

Lithology: Major:{gneiss}, Minor:{granitic}, Incidental:{anorthosite, syenite, diorite, amphibolite}

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]

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

Localities in this Region

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Crawford, James John (1894), Twelfth report of the State Mineralogist: California Mining Bureau. (Report 12): 12: 238.

Crawford, James John (1896), Thirteenth report of the State Mineralogist: California Mining Bureau. (Report 13): 13: 343.

Merrill, F.J.H. (1914), Geology and Mineral Resources of San Diego and Imperial Counties: Gems, Lithia Minerals. California State Mining Bureau, San Francisco, Cal. California State Printing Office. Chapter 2: 110.

Merrill, Frederick James Hamilton (1916), San Diego, Imperial Counties: California Mining Bureau. (Report 14): 14: 635-743; […(abstract): Geol. Zentralbl., Band 27: 395 (1922)]: 729-731.

Murdoch, Joseph & Robert W. Webb (1966), Minerals of California, Centennial Volume (1866-1966): California Division Mines & Geology Bulletin 189: 545.

Clark, Wm. B. (1970a) Gold districts of California: California Division Mines & Geology Bulletin 193: 162-163.

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