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U.S. Borax open pit (Boron pit), U.S. Borax Mine (Pacific West Coast Borax; Pacific Coast Borax Co.; Boron Mine; U.S. Borax and Chemical Corp.; Kramer Mine; Baker Mine), Kramer Borate deposit, Boron, Kramer District, Kern Co., California, USA

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Latitude & Longitude (WGS84): 35° 2' 40'' North , 117° 41' 40'' West
Latitude & Longitude (decimal): 35.0444444444, -117.694444444
The primary mineralization is borax, precipitated in a permanent shallow lake, fed from thermal (volcanic) springs rich in sodium & boron. Kernite was formed later upon deep (+1500 ft.) burial and temperatures above 53 deg. C (Christ and Garrels, 1959). The sodium borates together with claystone are hosted as a core facies within the Middle Miocene (16 mybp) Kramer beds (Barnard & Kistler, 1967) and are completely enveloped by ulexite-bearing shales (Gale, 1946). Stratigraphic and structural studies indicate the Kramer borates were deposited in a small structural, nonmarine basin, elongated in an east-west direction and limited on the south by the Western Borax fault.
[Joe Siefke 2010]

The open pit mine of the U.S. Borax Mine located in secs. 14 & 23, T11N, R8W, SBM, N of the town of Boron. A borate mine removing 10,000 tons/day during 1984. Owned by U.S. Borax & Chemical Corp.

In 1913 a borate mining claim was registered by O. Suckow, following identification of colemanite nodules during well drilling in the Kramer area of Kern Co. California.

This discovery claim was later bought out by the Pacific Coast Borax Company, whose subsequent exploration drilling in the district discovered the Na-borate deposit in 1925.

Their first exploitation was underground, via the shaft known as the Baker mine, which lies near the eastern end of the Na borate orebody. During 1926 & 1927, two other companies, Suckow Borax Mines and the Western Borax Co., began working further west in the deposit. Both of these operations were taken over within the next few years by Pacific Coast Borax [Western Borax in 1933].

In the late 1940's the former Western Borax property was bought by the California Borate Co. which since seems to have faded from the scene, although I can find no reference to it's demise. In 1956 Pacific Coast Borax merged with United States Potash Corporation, to become US Borax, and in 1957 changed from underground to opencast working.

The Jennifer Mine was a shaft located about halfway between the Western Borax and Suckow Borax mines, and is now included within the US Borax property. In 1968 US Borax became part of the Rio Tinto Group.

Zeolites occur in basalt underlaying the borate deposit.

Mineral List

35 entries listed. 28 valid minerals. 1 (TL) - type locality of valid minerals.

The above list 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.


Pemberton, H. Earl, Wm. Moller, Jack Schwartz & George Masimer (1960), The minerals of Boron, California, 40 pp. (Published by the Mineral Research Soc. of California, Montebello, CA): 27, 29, 33, 34.

Erd, R.C., V. Morgan & J.R. Clark (1961), Tunellite, a new hydrous strontium borate from the Kramer borate district, California: USGS PP 424-C, article No. 255: 294-297.

Murdoch, Joseph & Robert W. Webb (1966), Minerals of California, Centennial Volume (1866-1966): California Division Mines & Geology Bulletin 189: 102, 221, 228, 265, 283.

Morgan, V. and Erd, R.C. (1969) Minerals of the Kramer borate district, California California Division of Mines and Geology Mineral Information Service: 22: 152; Pemberton, H. Earl (1983), Minerals of California; Van Nostrand Reinholt Press: 246. , 255.

Pemberton, H. Earl (1983), Minerals of California; Van Nostrand Reinholt Press: 255.

Mining Annual Review (1985): 127.

Clays and Clay Minerals (1988): 36(2): 131-136.

Tschernich, R. (1992): Zeolites of the World: 64, 311.

American Mineralogist (2005): 90: 1186-1191.

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