A brief reconnaissance (5-8 November 2008) of the Big Sandy Formation near Wikieup (on US Highway 93 in Mohave County, Arizona) was undertaken to reconcile a reported dominance of lacustrine beds (Sheppard and Gude, 1972, 1973) with the largely terrestrial mammalian fauna reported from the formation (MacFadden et al., 1979; Lindsay and Mead, 2005). The issue is resolved satisfactorily by appreciation that nearly all fossil localities occur in fluvial beds that intertongue with and grade laterally into the dominant lacustrine strata.

To provide insight into provenance relations for multiple mid-Oligocene to mid-Miocene subbasins
(typically half-grabens) dissected by erosion in uplands lying north of the Catalina core complex and west of the San Pedro trough, 136 outcrop counts were made of clast types in tilted conglomerates of the Cloudburst and San Manuel Formations and their lateral equivalents in exposures as far north as the Gila River near Kearny. Clast counts were not made for younger conglomerates of the post-mid-Miocene Quiburis Formation, which fills the San Pedro trough and onlaps flanking uplands (Dickinson, 1998), because Quiburis clast assemblages in all cases match bedrock sources exposed uphill on the modern landscape. By contrast, paleotopography during Cloudburst and San Manuel deposition can only be inferred from local paleocurrent indicators (clast imbrications; figure 39 of Dickinson, 1991, p. 70-71) and clast assemblages in tilted strata. Areas included in this study were the Guild Wash allochthon between the Tortolita and Suizo Mountains, the Star Flat allochthon on the east flank of the Black Mountains, the
Black Hills (west of Mammoth), Camp Grant Wash (and Putnam Wash) between the Black Mountains and the Black Hills, multiple drainages of the Tortilla Mountains (Eagle Wash, Jim Thomas Wash, Hackberry Wash, Indian Camp Wash), and Ripsey Wash on the west flank of the Tortilla Mountains (Figs. 1-4).