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CALIFORNIA

Lost Amargosa Diggings

GEOLOGY OF THE AREA

The area of interest encompasses much of the southern portion of Death Valley. This extensive region of deserts and mountains consists mostly of uplifted Precambrian basement rock intruded by younger Mesozoic granites and still younger Tertiary volcanics. The Salt Spring Hills, site of the old Amargosa Mine, consist of highly eroded Precambrian metamorphic and sedimentary rocks, Cambrian marine sediments, some Permian marine sediments, and a small exposure of Mesozoic-age granite. Likewise, the Saddle Peak Hills, Ibex Hills, and Black Mountains are all mostly composed of Precambrian metamorphic and sedimentary rocks.

The Owlshead Mountains are a curious, nearly circular range of eroded hills located west-southwest of the Black Mountains. The Owlshead Mountains are mostly composed of older Mesozoic-age granites and younger Tertiary and Quaternary-Tertiary volcanics.

The Calico Peaks area and Sheephead Mountain lie just north of the Ibex Hills. This range of hills is composed of Miocene and Pliocene volcanics. The Avawatz Mountains, located just south of the Salt Spring Hills and the Amargosa Mine, are another uplifted block of Precambrian metamorphic basement rock. The range is host to several small Mesozoic-age granitic stocks.

Death Valley, which trends northwest-southeast in this area, coincides with a major fault, the Death

Valley Fault Zone. The Amargosa River flows through this valley. Further south, in the Silver Lake area (located 20 miles south-southeast of the Amargosa Mine), the surrounding hills are underlain by ancient Precambrian basement rock intruded by younger Mesozoic-age granites.

The intervening basins, playas, and canyons are filled with Quaternary alluvium first and foremost, but some Quaternary sand dunes and lake deposits are present. A small field of aeolian sands (less that 1 square mile) lies between the Salt Spring Hills and the Amargosa River. Just northeast of the Salt Spring Hills lie the famous Dumont Sand Dunes. The abandoned site of Dumont is located near the eastern edge of the dunes.

In general, the area of interest displays classic Basin and Range Province geology. The mountain ranges are uplifted fault-blocks consisting mostly of Precambrian metamorphic and sedimentary basement rock intruded by younger Mesozoic granitic plutons and stocks and younger still Tertiary and Quaternary-Tertiary volcanics. Occasionally, upthrown wedges of early Paleozoic (Cambrian) and late Paleozoic (Permian) marine sedimentary rocks occur in the hills and mountains of the region.

PROSPECTING POTENTIAL

The vast amount of country encompassed by the Amargosa watershed presents a daunting prospect for the hardy gold-seeker. Certainly the most promising areas are in the vicinity of the Amargosa Mine and the dry washes and arroyos that drain the slopes of the Salt Spring Hills. But gold is where you find it and so the persistent prospector may want to investigate those sections of the river that

coincide with the old Death Valley Trail used by the early emigrants. McCloskey and his bride were camped near the Amargosa when he made his discovery. As with most placer deposits, a metal-detector may be useful in the search. Prospectors should realize that much of the area of interest lies within Death Valley National Monument.