The Sierra Ancha are a series of high plateaus, mesas, and ridges that extend from Theodore Roosevelt Lake in the south to the Mogollon Rim on the north. The southern margin is in some paces a steep escarpment or series of escarpments, in part defined by normal faulting and down-dropping of blocks to the south and by relatively little faulting to the north. Faulds (1986) and Potochnik (1996) suggested that the southern margin of the Sierra Ancha is an ancient paleocanyon through which the ancestral Salt River flowed to the east. Deep, narrow canyons separate the mesas. Some of the deeper canyons reveal older, early Proterozoic (~1.7 Ga) metamorphosed sedimentary and volcanic rock and weakly deformed early and middle Proterozoic granitic rocks. However, most of the Sierra Ancha are composed of very weakly metamorphosed to unmetamorphosed, nearly flat-lying sedimentary rocks of the middle Proterozoic Apache Group.