File:Hot spring & Hot Creek (Long Valley Caldera, California, USA) 15.jpg

English: Hot Creek is in eastern California's Long Valley Caldera, a large depression formed about 760,000 years ago during a large eruption of the Long Valley Volcano. The eruption produced large volumes of ash, air-fall pumice, and pyroclastic flow pumice.

As the name suggests, Hot Creek's valley has hot springs - hydrothermal water emerges at the surface along an intracaldera extension of the Hilton Creek Fault.

The bedrock in the Hot Creek area includes the Hot Creek Rhyolite Flow, a sanidine-augite-phyric moat rhyolite that erupted from a vent to the south of here. The Hot Creek Flow dates to ~288 ka or ~333 ka (= Pleistocene).

Description of Hot Creek Rhyolite lithologies at Hot Creek Gorge (from Hildreth & Fierstein, 2017): ". . . the rhyolite is flow-foliated, locally vuggy, and variously includes pale-gray to black vitrophyre, bluish-gray resinous perlite, gray to pink felsite, coarsely pumiceous carapace, dark brown spherulitic zones, and flow breccia. Cream-white domains can be either felsite, finely vesicular glass, or silicified. Strongly oxidized and hydrothermally altered exposures are common along the gorge. . . . The rhyolite contains only ~1 percent phenocrysts, of which half are plagioclase, accompanied by trace amounts of sanidine, biotite, and clinopyroxene, as well as microphenocrysts of Fe-Ti oxides, zircon, and apatite."

In the vicinity of the hot springs, surficial travertine deposits are present. Travertine is a chemical sedimentary rock composed of calcium carbonate. It is the dominant lithology in "cave formations" (= speleothem) and many cold spring and hot spring deposits.

Locality: Hot Creek Gorge, Long Valley, eastern California, USA (37° 39' 39.56" North latitude, 118° 49' 43.67" West longitude)

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Reference cited:

Hildreth & Fierstein (2017) - Geologic field-trip guide to Long Valley Caldera, California. United States Geological Survey Scientific Investigations Report 2017-5022-L. 119 pp.