Active and Fossil Rhyolite-Hosted Epithermal Systems of the Mojave Desert
Our trip departs from San Diego near the border between the United States and Mexico. Unfortunately we have a long trip to the first major stop, but you will get a chance to see a lot of Southern California geology and scenery along the way.
Proceeding north along route 15/215 we pass through the hills and valleys of the relatively lush coastal region and into the more typical semi-arid interior of southern California. Knobs of granitic rock belonging to Peninsular Ranges Batholith can be seen separating the valleys in which irrigated farms and housing developments abound. Much of the water used for both of these is imported, either from the Colorado River to the east, or from the Owens Valley, near the destination of todays' drive.
As we approach the city of Riverside, larger mountains become visible to the north and east. These are the San Jacinto mountains to the east and the Transverse Ranges (San Bernardino and San Gabriel mountain ranges) to the north which reach elevations of over 10,000 ft. thanks to the prodding of the San Andreas Fault Zone.
Nearing the city of San Bernardino we cross the San Jacinto Fault (one of the more active strands of the San Andreas transform fault trend) conveniently located directly beneath the interchange for the 10 and 215 freeways.
We then climb up into the Cajon Pass where we cross the main strand of the San Andreas Fault, forming a saddle between the San Gabriel mountains to the west and
Figures & Tables
The Kramer borate deposit is located in the northwestern Mojave Desert, about 90 air miles northeast of Los Angeles and 3 miles north of the town of Boron (figure 1). The deposit derives its name from the mining district in which it lies. The Kramer deposit, presently being mined from the Boron open pit, has been a world-class source of sodium borates since mine startup in 1926 and continues to be the largest source of borates in the world.
The Kramer ore body is a roughly lenticular sedimentary sequence of borax (Na2B4O7 • 10H2O) and kernite (Na2B4O7 • 4H2O) containing interbedded claystone. This central crystalline facies is successively enveloped by facies consisting of ulexite (Na,CaB5O9 • 8H2O) -bearing claystone, colemanite (Ca2B6O11 • 5H2O) -bearing claystone, and barren claystone. Studies indicate the Kramer borates were deposited in a small structural, nonmarine basin, associated with thermal (volcanic) spring activity during Miocene time.
The Kramer deposit does not crop out. It was discovered accidentally in 1213 by Dr. John Suckow, a homesteader, who struck colemanite while drilling a water well (figure 2). Exploratory drilling and shaft sinking after World War I by Pacific Coast Borax Company, the predecessor of U.S. Borax, led to the discovery of borax and kernite in 1925. In 1926 PCB went into large-scale, underground sodium borate mining in the Baker mine, located nearly 2 miles east of Suckow's discovery well. The company soon closed all its calcium borate operations near Ryan in Death Valley in favor of the more easily processed sodium borates at Boron.
U.S. Borax ships mostly bulk, refined sodium borate products and boric acid to both domestic and world markets from Boron. Principal uses for these products are in the manufacturing of glass and fiberglass, herbicides, ceramics, soaps and detergents, fluxes, fertilizers, and fire retardants.