1) OLIGOCENE GLEN CANYON ERODED BY COLORADO RIVER DURING EXCAVATION OF EOCENE FILL IN GRAND CANYON; 2) NEOGENE SUBSURFACE FLOW OF COLORADO RIVER THROUGH GRAVEL PIPELINE IN GRAND CANYON, KAIPAROWITS PLATEAU TO GRAND WASH CLIFFS, UTAH-ARIZONA
2) Stratigraphic-geomorphic studies across Cent. and N. Arizona indicate that a semi-arid to arid Neogene environment characterized all but latest Pliocene time. Local erosion and deposition, resulting from sporadic storms, widely aggraded Oligocene stream courses and basins with flash-flood and playa deposits (gravels, mudstones, evaporites, and marly lake beds). Lastly, a very strong (Verde-Hualapai) pluvial in the interval 3-1.8 Ma led to formation of numerous lakes; erosion of Neogene deposits followed their overflow. Eastern Grand Canyon at Hilltop Ruins had been completely blocked by more than 400' of Neogene gravels, all but the basalmost locally derived. Correlative deposits more than 1500' thick also had accumulated against Grapevine Mesa (lower Grand Wash Cliffs); although 120 miles away, limestone at its top is only 250' lower than Hilltop gravels (gradient 2'/mi). Subsurface flow through a gravel pipeline provides both a source and means for precipitating the numerous thick beds of salt found in Neogene deposits of the Southern Basin and Range.