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2020 - Trip Report - Geology of Salt Creek Hills

Geology of Salt Creek Hills

By Bill Neill

The Amargosa region has complex and beautifully exposed geology, and displays the geological history of much of western North America.  A good place to start a virtual tour is at Salt Creek Hills, located near Highway 127 midway between Baker and Shoshone.

The oldest rock unit at Salt Creek Hills is Paleozoic limestone, deposited from tropical seas on a slowly subsiding continental shelf.  The continental margin of western North American formed and then subsided after a larger continent was split away by rifting, and the separated mass now probably forms Australia or Antarctica.  In places the Paleozoic limestone abounds with fossil marine shells, which ancient animals evolved as armor for protection from predators.

In the Grand Canyon, Paleozoic limestone and sandstone layers of similar age are relatively thin and undeformed; whereas the units thicken to the west, forming a wedge-shape geometry, and are faulted and folded from later compressional impacts to the continental margin.  These uplifted sedimentary layers underlie much of the Nopah and Resting Springs Ranges east of Shoshone, plus the mountain ranges bordering the north half of Death Valley.

About 450 million years after deposition, and after folding and faulting, the Paleozoic layers near the south end of Death Valley were intruded by molten rock – magma - that fed volcanoes at the surface.  The magma crystallized slowly to form coarse-grained granite, light in color because its chemical composition was high in silica and low in iron.  The granitic rock is of Jurassic age, somewhat older but similar in origin to granitic rock that underlies the Sierra Nevada.  During this period, California resembled the current western edge of South America, where a major volcanic chain – the Andes – results from subduction of an oceanic tectonic plate offshore.

As the granitic magma crystallized, hydrothermal fluids carried metals including iron and gold into the overlying limestone and formed a small gold ore deposit.  In 1849, forty-niners headed west to the California Gold Rush via the southern route – the Old Spanish Trail from Utah – noticed gold specks in Kingston Wash and eventually started mining at the contact between granite and limestone.  In 1851 a rock building called the Amargosa House was constructed nearby that is the oldest structure in San Bernardino County.  This history is described in the second chapter of Richard Lingenfelter’s 1986 book Death Valley & The Amargosa – A Land of Illusion.

Today the Salt Creek Hills are valuable ecologically as riparian wildlife habitat, where Kingston Wash cuts through the granite hills and provides small amounts of surface water throughout the hot summers.

A small spring named Amargosa Spring and the adjacent gold mine area can be visited by a one-mile hike from the parking area near Highway 127.  A well-marked trail crosses the narrow wash with reeds, mesquite and a large Athel grove, then continues northward to the Amargosa House and remains of a 1880s stamp mill.

A field trip to Salt Creek Hills will be part of our Meet the Amargosa weekend next October 25-27 based in Shoshone.                                           ~ Bill