Figure 10. Geologic map of the paleovalley at Nanny Creek, east side of the Pequop Mountains (Brooks et al., 1995b; this study) with ⁴⁰Ar/³⁹Ar dates from this study (regular type) and Brooks et al. (1995a, 1995b; italics). The paleovalley, which was at least 6 km wide and possibly 1.6 km deep, has basal conglomerate containing rounded boulders up to 6 m in diameter, overlain by the plagioclase-biotite tuff and tuff of Big Cottonwood Canyon, andesite lavas, and a thick megabreccia consisting of angular blocks mostly of the tuff of Big Cottonwood Canyon. That megabreccia consists of reworked blocks is confirmed by petrographic, chemical, ⁴⁰Ar/³⁹Ar, and paleomagnetic data (this study; M.R. Hudson, in Brooks et al., 1995a; Palmer and MacDonald, 2002).