CROOKED RIDGE RIVER (CRR) REDUX

Information on pre-incision drainage on the Colorado Plateau is scanty, so the wind gap in the Echo Cliffs at The Gap has long been of interest. Far-traveled clasts in the area were attributed by early geologists to a river originating in the San Juan Mtns., but the course was not known. Satellite and DEM data now show the sinuous course of the river on the Kaibito Plateau in inverted relief.

On the basis of these new data, Lucchitta et al. (2013) concluded that

• The river originated in the San Juan Mtns. because it carried clasts of all lithologies exposed along its course from these mountains to the Kaibito Plateau
• CRR was the master stream of the area because no other ancient river courses are visible on the Kaibito Plateau or the Echo Cliffs
• The valley of the river was wide (10-15 km) and at least 270 m, but possibly ~700 m deep on the basis of clasts in the alluvium derived from the valley walls
• The alluvium now exposed is the last deposited by CRR before it died, as shown by the massive calcrete that overlies it.
• The initial age of the river was not known, but probably was much older than the present alluvium and possibly Oligocene because the river issued from the high San Juan Mtns. of that age

Hereford et al. (2016) then proposed instead that

• The exotic clasts in CRR came from reworking an older nearby piedmont gravel
• CRR was a local stream
• The river valley was not especially large
• All the alluvium on White Mesa and Crooked Ridge was deposited by local, not regional, streams
• The river was early Pleistocene on the basis of an interbedded 2 Ma tuff

We disagree

• No older piedmont gravels containing exotic clasts are exposed, documented, or even known
• Several of the clast lithologies would not survive recycling
• CRR was the master stream of this area because other old streams are not known and the other paleochannels on White Mesa contain only rare or no exotics, so likely are tributaries
• The alluvium of CRR is the important stratigraphic unit because that in the other channels is of only local origin
• CRR died sometime after 2 Ma, but was born much earlier

Conclusions: CRR was a master stream that originated in the San Juan Mtns., was born possibly in the Oligocene, eroded The Gap, crossed the Kaibab upwarp with the Colorado River (and the Little Colorado River?) along the alignment of the eastern Grand Canyon, and finally died sometime after 2 Ma.