Unit unconformably overlies newly named Idavada Volcanics in foothills 7 mi northwest of Murphy, at Sinker Creek, 8 mi south of Murphy and along lower Squaw Creek, 2 mi east of U.S. Hwy 95 near northern end of Owyhee Mountains (near Homedale), northwest Owyhee Co, ID, Snake River basin. Thickness is 400 ft northwest of Murphy. Near Murphy, unit overlain by Banbury Basalt; near Homedale, overlain by Glenns Ferry Formation (new). Assigned as lowermost of seven formations of Idaho Group (rank raised). Early Pliocene age based on mammalian fossils.
[NOTE: The Department of the Interior's Secretarial Order 3404, issued on November 19, 2021, formally identifies the term “squaw” as derogatory. That Order will create a federal Derogatory Geographic Names Task Force, to find replacement names for geographic features in use by federal agencies. We’re awaiting guidance from the Task Force, and will then take the appropriate actions.]

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

Pg. 236. Poison Creek Formation of Idaho Group. E.H. McKee (written commun., 1971) reports that four dates on overlying Banbury Basalt of Idaho Group in Owyhee-Jarbidge region, southern ID, range from 8.0 to 10.6 Ma, older dates being preferred. On this basis, Poison Creek is considered about 11 Ma; North American land mammal age Clarendonian [=lower Pliocene (Evernden and others, 1964, Amer. Jour. Sci., v. 262, p. 145-198), =Miocene (Berggren, 1972, Lethaia, v. 5, no. 2, p. 195-215)]. Report includes sample locality map, schematic stratigraphic-chronologic diagram, table of K-Ar ages.

Source: Publication.