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Darrel Cowan: Reaching out to non-geologists

Aug 17, 2022 | Board Blog

Darrel S. CowanI’m Darrel Cowan. In addition to being a geologist and emeritus professor of Earth & Space Sciences at the University of Washington in Seattle, I also have the pleasure of serving on the Friends of the Amargosa Basin Board of Directors. I want to share with you what particularly interests me about this special area. I recall my first trips to Death Valley were on short family vacations from Los Angeles as a kid in the early 1950s. I knew nothing about geology or rocks, but I’m sure that these visits engendered my passion for the deserts in southern California. My first trips to indulge in the geology were in an undergraduate class at Stanford: Geology of California. In those days, we could camp anywhere, even in the sand dunes near Stovepipe Wells! My first visit to Shoshone was in a graduate class in sedimentary geology. We camped in the Tecopa lake beds, and hiked up a ridge on the east flank of the Nopah Range. I can assure readers that on that trip, I never could have predicted that I would return to the Amargosa Basin or become a part-time resident of Shoshone.

By the early 1990s, I began my own research and supervision of graduate students in the region. I still bring my Structure & Tectonics class to Shoshone every March, and I lead short trips for other groups that include photographers and biologists in addition to rock jocks.

I’d like to invite readers of diverse backgrounds, even those with only a brief contact with geology, to understand why geologists of all stripes consider the Amargosa Basin—and Shoshone—as a mecca. My first blog regarding the geologic wonders of the Amargosa Basin focuses on early earth history, from about 1.7 billion to 400 million years ago. Geologists use rocks as a record of geologic events: earth history is preserved in the rock record. Rocks in this age range are widely exposed in Death Valley National Park; however, rock units present in the Amargosa Basin are especially complete and easily accessible. I created a stratigraphic column of the important rock units in the basin for a sign viewable to the public right outside the Shoshone Museum. This stratigraphic column is a diagrammatic representation of layered sedimentary rocks as they were originally deposited in the ocean basin that once existed in the region.

If one looks east from Shoshone at the western front of the Resting Spring Range, some of the formations in the column are spectacularly exposed. These layers—strata—were originally deposited horizontally in the ocean but have been tilted and exposed by faulting: a topic for a future blog. Compare this view with the stratigraphic column and note the ages. The brown layers at the base of the range front are the Wood Canyon Formation. They contain the earliest forms on earth of hard-shelled organisms, the trilobites, which are in the same animal group as arthropods. Next above is the pink stripe of the Zabriskie Quartzite, then the brown and dark gray Carrera limestone. Above is the distinctively striped Bonanza King Formation, limestone full of fossils such as corals. The strata lower in the column, but not visible here, and hence older, also contain a record of earlier life.

Stratigraphy of Shoshone Tecopa

Stratigraphic column diagrammatically depicting the sequence of layered rock units in the Amargosa Basin. The colors do not represent the actual colors of the units. A brief description of the major rock types accompanies the formal name as do the approximate ages of the units.

Shoshone Tecopa

The western front of the Resting Spring Range while standing on CA 178 about two miles east of Shoshone. The colors of the four exposed rock units are so distinctive that you will recognize them in other ranges in the Amargosa Basin, including the Dublin Hill, the Nopah Range, and Eagle Mountain.