Well exposed in Wasson Canyon and in amphitheater north of Brest Mountain (T38S R2E), Jackson Co, southwestern OR. Named applied to sequence of tuff beds and flow breccias that form upper part of Little Butte volcanic series (new). Most conspicuous layer of sequence is chalky white tuff about 200 ft thick; below this tuff and separated from it by about 300 ft of platy andesite flows and agglomerates is 300-ft bed of massive, dirty-yellow tuff consisting of angular fragments in basaltic tuff matrix. Leaf prints were found in tuff (sec.25 T36N R2E). Overlies Roxy formation (new); capped by Heppsie andesite (new). Geologic map of Medford quad shows several distinct lithologies. Age is late Oligocene based on fossil flora.

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

Mapped with Mehama volcanics of Thayer (1933, Pan-Amer. Geol., v. 59, no. 4, p. 317), Breitenbush tuffs of Thayer (1936, Jour. Geol., v. 44, no. 6, p. 704, 705, 709 (fig. 2), 713 (fig. 3)) [1939, Oregon Dept. Geol. and Min. Ind. Bull., no. 15, p. 9-10, fig. 1 (geol. map)], upper part of Fisher formation (H.E. Vokes and others, 1951, USGS Oil and Gas Inv. Map OM-110), upper part of Calapooya formation, Eagle Creek formation, and Molalla formation of Harper (1946, Oregon State Univ., unpub. MS thesis, 26 p.). Age for all units is Oligocene and early Miocene.

Source: Modified from GNU records (USGS DDS-6; Menlo GNULEX).

Included as uppermost formation (of 3) of Western Cascades Group. Rocks formerly called "beds of Bogus Mountain" of Hammond (1983). Geologic sketch map of portion of Copco 15' quad in northwestern CA show unit includes (ascending); Bogus Tuff and Lakeview Tuff [informal ash-flow tuffs]. Consists of several distinctive ash-flow tuffs together with interbedded lavas and fluvial sedimentary deposits. Overlies Roxy Formation; unconformably underlies Pliocene and Quaternary lavas of High Cascades Group. Fission-track and K-Ar ages on Wasson ash flows yield between 26 and 21 Ma. Fission track age of 20 Ma was determined on zircon and apatite from pumiceous tuffs high in upper part of Western Cascades Group, thus indicating upper part of unit is latest Oligocene to very early Miocene age.

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