Named as middle of three formations of Laguna Springs Volcanic Group (revised; raised in rank) for exposures east of Pinyon Queen shaft in secs 34 and 35, T9S, R2W, Utah Co, UT (its type locality) on Wasatch uplift. Consists of two informal members: 1) a lower tuff member, ranging from soft, fine-grained, sandy tuff to boulder agglomerate. Includes a basal zone characterized by cobbles and boulders of vitrophyre and other rocks embedded in fine-grained, ashy tuff. This agglomerate is overlain by lenses of unsorted lapilli tuff; and 2) an upper flow member, massive, medium- to coarse-grained latite porphyry, dark-reddish-brown. In some areas magnetite is fairly abundant. K-Ar date on biotite is anomalously young when compared with over- and underlying formations dated at about 32 m.y.; is considered middle Oligocene based on position. The basal tuff member was erupted over an irregular topography, so ranges in thickness from 6 in to 400+ ft. Chiefly overlies Packard Quartz Latite, but north of North Standard shaft is locally underlain by North Standard Latite (new) of Laguna Springs Volcanic Group; near Wing Spring it overlies Latite Ridge and Big Canyon Latites of Tintic Mountain Volcanic Group (all new). Upper flow member is incomplete in all exposures due to erosion. Maximum thickness of 700 ft. Underlies Tintic Delmar Latite (new) of Laguna Springs Volcanic Group. Geologic map, measured sections, stratigraphic chart.

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