Named as a member of Plateau Rhyolite (new) for exposures on steep slopes west of Shoshone Lake, Yellowstone National Park, Yellowstone province, WY. Type section is in gully north of Fall Creek, west of Shoshone Lake Geyser basin where the member is about 180 m thick and lies between two flows of Central Plateau Member (new) of Plateau Rhyolite. Is an ash-flow tuff that is glassy, nonwelded to partially welded. Has local vapor-phase and devitrified zones in upper part. Irregular distribution suggests emplacement on a lake of glacial ice. Source area was in vicinity of West Thumb. Contains 20-30 percent phenocrysts of quartz, sanidine, subordinate plagioclase, and minor clinopyroxene and opaque oxides. Inclusions of older rhyolite, mainly black vitrophyre, abundant throughout member. Age bracketed by two flows of Central Plateau Member, i.e., 200,000 to 150,000 years old, respectively, and by sanidine from tuff in member of 180,000 years.

Source: GNU records (USGS DDS-6; Denver GNULEX).

Shoshone Lake Tuff Member of Plateau Rhyolite abandoned; its rocks now included in unnamed tuffs of Cold Mountain Creek (Old Faithful quadrangle) and Bluff Point (Norris Junction quadrangle) and assigned to Central Plateau Member, uppermost member of Plateau. Study area in Yellowstone National Park, Wyoming.
See also R.L. Christiansen, 1974, Geol. map West Thumb quad., Yellowstone Natl. Park, WY, USGS Geol. Quad. Map GQ-1191; R.L. Christiansen, 1975, Geol. map Norris Junction quad., Yellowstone Natl. Park, WY, USGS Geol. Quad. Map GQ-1193.

Source: Changes in stratigraphic nomenclature, 1975 (USGS Bull. 1422-A, p. A36-A37).