A PROPOSED LARAMIDE PROTO-GRAND CANYON

The absence of "rim gravels" north of Grand Canyon and of Canaan Peak-type gravels south of Grand Canyon suggests that a paleo-canyon, which intersected the transport of gravels north and south, may have existed during the Laramide in approximately the same position as today's central Grand Canyon. In the Paleogene this paleo-canyon drainage is envisioned as having flowed northeast from the Peach Springs-Music Mountain area, where it was incised to at least the Tapeats Sandstone level; north along the Hurricane monocline to about River Mile 198; then northeastward down the east flank of the monocline to near the vicinity of Kanab Point, where it was incised to perhaps the Kaibab Limestone level. At Kanab Point this drainage confluenced with westward-flowing drainage off the Kaibab arch that was partly constrained along the Grandview monocline. From this confluence, it then proceeded northward over a probable Mesozoic terrain along the west flank of the Kaibab arch to Lake Claron in southern Utah, with northwest-trending tributaries flowing off the arch to this drainage (the northwest pattern of streams still present today from Lookout Canyon northward). Then in the Miocene, when a drainage reversal from north to south commenced with Basin and Range faulting, a stream followed this old paleo-canyon route southward along the west flank of the arch, depositing Canaan Peak-type quartzite cobbles along Johnson Creek, Cedar Knoll-Little Cedar Knoll, and the Goosenecks. After Basin and Range-age faulting specifically began along the Gunsight Point-Kanab Creek fault system, this reversed southward drainage system progressively "slid" down to its present position along Kanab Creek. The basic idea suggested by this proposed model is that the modern Colorado River utilized Laramide paleo-topography to establish its course across the central Grand Canyon. Headward erosion from the Grand Wash Cliffs after 16 Ma could have rapidly followed this paleo-canyon route, thus helping to account for the total volume of rock eroded from Grand Canyon, which cannot be explained by present-day incision rates.