Pg. 6, geologic time scale (inside front cover). fanglomerate of Osborne Wash. Sample from "Headgate Rock" olivine basalt, lower basalt in fanglomerate of Osborne Wash, in NE/4 sec. 31, T. 10 N., R. 20 W., Lat. 34 deg. 10 min. 00 sec. N., Long. 114 deg. 16 min. 30 sec. W., Parker quadrangle, Yuma County, Arizona, yielded a K-Ar age of 12.9 +/-0.6 Ma (whole-rock), minimum age of extrusion. Sample from olivine basalt, in upper flow in fanglomerate of Osborne Wash, at Lat. 34 deg. 11 min. 00 sec. N., Long. 114 deg. 13 min. 30 sec. W., in NW/4 sec. 27, T. 10 N., R. 19 W., Cross Roads quadrangle, Yuma County, Arizona, yielded a K-Ar age of 8.5 +/-0.2 Ma (whole-rock), minimum age of extrusion. Ages calculated using decay constants of Steiger and Jager, 1977 (Earth Planet. Sci. Letters, v. 36, p. 359-362). [Miocene, based on time scale of Berggren, 1972, Lethaia, v. 5, no. 2, p. 195-215.]

Source: Publication.

Pg. 119, 122. Osborne Wash Formation. Consists of basal fanglomerates, basalt flows interbedded with agglomerate, tuff, and alluvial fan deposits; intrusive dikes and plugs. Thickness is greater than 400 m. Basal fanglomerates and air-fall tuffs have filled old valleys with relief of at least 300 m; unit deposited after detachment faulting. Unconformably overlies the Gene Canyon and Copper Basin Formations and older crystalline rocks. Age is Miocene to Pliocene(?).
Type locality not stated. Widespread exposures in western Buckskin Mountains, Yuma Co., AZ, and in southeastern Whipple Mountains, San Bernardino Co., CA. Origin of name not stated by authors, but probably named from exposures in hills near Osborne Wash, where AZ Highway 95 bridges the wash northeast of Parker, Yuma Co., AZ.

Source: US geologic names lexicon (USGS Bull. 1564, p. 122); supplemental information from GNU records (USGS DDS-6; Menlo GNULEX).