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

1) Geomorphic-stratigraphic-structural interrelations from the Kaiparowits to Paria Plateaus indicate: 1) the north-dipping Early Cretaceous Paria erosion surface traces into an unconformity overlain by the early Late Cretaceous Dakota Sandstone; 2) northward, a near-horizontal surface of the Late Cretaceous (Cenomanian-early Campanian) Kaiparowits Plateau (Laramide a) overlooks a two-step (Laramide b-c) escarpment and an entrenched Oligocene Glen Canyon; the surface traces westward to the margin of the Central Plateau where it is unconformably overlain by conglomeratic strata of the early Campanian to Paleocene Canaan Peak and Pine Hollow Fms.; 3) the Cretaceous erosional landscape at Marble Canyon then was buried by 3700' + of basal conglomerates and sediments of Arizona's Eocene Rim gravels (=Claron-Wasatch Fm.); and, 4) a meandering south-flowing Oligocene Colorado River, entrenched in Eocene sediments, eroded Glen Canyon beneath an uplifted Laramide c surface. Relict consequent tributaries leading into Glen Canyon prove its post-Eocene erosion. South of the Cent.-S. Plateau boundary at Lees Ferry, the Oligocene Colorado River escaped to the S. Basin and Range by excavating soft Eocene fill from a Late Cretaceous Marble-Grand Canyon.

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.