Implications of the Miocene(?) Crooked Ridge River of northern Arizona for the evolution of the Colorado River and Grand Canyon

Abstract

The southwesterly course of the probably pre-early Miocene and possibly Oligocene Crooked Ridge River can be traced continuously for 48 km and discontinuously for 91 km in northern Arizona (United States). The course is visible today in inverted relief. Pebbles in the river gravel came from at least as far northeast as the San Juan Mountains (Colorado). The river valley was carved out of easily eroded Jurassic and Cretaceous rocks whose debris overloaded the river with abundant detritus, probably steepening the gradient. After the river became inactive, the regional drainage network was rearranged three times, and the nearby Four Corners region was lowered 1-2 km by erosion. The river provides constraints on the early evolution of the Colorado River and Grand Canyon. Continuation of this river into lakes in Arizona or Utah is unlikely, as is integration through Grand Canyon by lake spillover. The downstream course of the river probably was across the Kaibab arch in a valley roughly coincident with the present eastern Grand Canyon. Beyond this point, the course may have continued to the drainage basin of the Sacramento River, or to the proto-Snake River drainage. Crooked Ridge River was beheaded by the developing San Juan River, which pirated its waters and probably was tributary to a proto-Colorado River, fl owing roughly along its present course west of the Monument upwarp.

Crooked Ridge River (Crr) Redux

“…Taken together, these zircon ages indicate provenances that match well and reinforce those indicated by the clast lithologies in the CRR gravel as given by Lucchitta et al (2013, Tables 1 and 2). When these provenances are combined with physical characteristics of the CRR alluvium, which indicate that the paleoriver flowed toward the southwest, the clear conclusion is that the river originated in the San Juan Mountains, as indicated by Lucchitta et al (2013).…”

“…When these provenances are combined with physical characteristics of the CRR alluvium, which indicate that the paleoriver flowed toward the southwest, the clear conclusion is that the river originated in the San Juan Mountains, as indicated by Lucchitta et al (2013).…”

“…Data from Lucchitta, et al, 2013 andDickinson, et al, 2010: • Gravel deposits at Crooked Ridge contain abundant pebbles and cobbles of lithologies characteristic of: San Juan Mtns. volcanic, plutonic and metamorphic rocks; Colorado Plateau diatremes; Colorado Plateau laccoliths.…”

“…Holm, B.K. Lucchitta, and Ivo Lucchitta, who had long been interested in the possibility of an ancient and far-reaching river here, undertook to investigate it, naming it Crooked Ridge River, CRR, (Lucchitta et al, 2013).…”

“…Lucchitta et al (2013) concluded that ancestral Crooked Ridge river carried clasts of all lithologies exposed along its course from the San Juan Mountains to the Kaibito Plateau Figs. 1, 2 and 4) Hereford et al (2016) cited Cather et al (2008) for the basis of their idea that the exotic pebbles at Crooked Ridge were recycled from ancient gravel deposits on a regional piedmont described and depicted by Cather et al, 2008, Figure 14, p. 28.…”