Black Rock country is truly one of the most fascinating landscapes in North America. Nestled between the western edge of the Basin and Range Province, the Black Rock Desert forms a unique assemblage of volcanic lava flows, ash, ancient shallow marine sea floor, exotic batholithic terrain, and lacustral sedimentary packages.
Within the Black Rock, the most striking and prominent feature is a silt alkaline Salt Pan, commonly referred to as a playa. The Black Rock Playa, elevation 3,848 ft, is the second-largest flat region in the Northern Hemisphere. Shaped like a “Y”, the Black Rock can be divided into 3 parts: the playa, west arm, and east arm.
The longest stretch of playa is 27 miles along the west arm. South of the intersecting arms, the widest spot is 12 miles. The playa has a “bulge” in the middle that is widely reported to be the visible curvature of the earth; this is actually the result of water pressure and the expanding clays that make up the playa fill. (The earth’s curvature is not visible from altitudes lower than about 20 miles.)
Also unique to Black Rock is a large concentration of hot springs, found along the escarpment of the ranges bordering the playa. The source of the springs is still unknown, although it is theorized that they are the result of active volcanism and latent heat from the Cascades in northern California and Oregon.
The playa is the remnants of Pleistocene Lake Lahontan, which at its greatest expanse 13,000 years ago covered 8,665 square miles of northwestern Nevada. Over the last 75,000 years Lake Lahontan has had four measurable high stands which all correlate to glacial advances in the Sierra Nevada.
The highest lake stand was during the most recent glacial period. Geologic evidence suggests depths up to 920 ft. at what is now referred to as Pyramid Lake, 525 ft. in Walker Lake, and 490 ft. in the Carson Sink. Lush vegetation and an abundant water supply were present, provided from rivers draining off the Sierra Nevada Mountains & Modoc Plateau. Giant mammoth, camels, horses, and saber-toothed tigers roamed the marshy land.
In 1979, the largest mammoth ever found was discovered in the Black Rock Desert located in a channel of the Quinn River. This 17,000 year-old Imperial Mammoth was 50 years old at death, weighed 13,000 pounds, and was 13 ft. tall at the shoulders.
Glacial retreats, subsequent extension of the Basin and Range, and further development of the California Coastal Ranges, Sierras, Cascades and Klamath Mountains created physical barriers generating a Rain Shadow habitat in northwestern Nevada and eastern Oregon. Lake Lahontan eventually dried up, leaving behind terraces (up to 300 ft. wide) on the surrounding mountains and the current playa surface.
– Thanks to Catherine O’Riley, Mike Bilbo (BLM), and Nate Pepel.
Suggested Reading: Geologic and Natural History Tours in the Reno Area (1995), Purkey, Becky Weimer, University of Nevada, Reno, Mackay School of Mines