666 WHITMAN CROSS 
The pebbles of the conglomerate strata of this section are principally 
of granite and the most abundant variety is the very coarse-textured 
one with large orthoclase crystals occurring in the nearest exposures 
of the Uncompaghre Plateau. Among the pebbles are some of 
greenstone schist which indicate that the pre-Cambrian complex 
furnishing this material is similar to that from which the Cutler con- 
glomerate of the San Juan was derived. Similar greenstones were 
observed in the conglomerates of Grand River Valley. 
Below the measured section there may be several hundred feet of 
similar strata, for the somewhat deeper cutting of Dolores River does 
not reveal the base of the succession of grits and conglomerates. The 
next lower formation is probably a series of gypsiferous shales and 
sandstones and the nearest locality at which such strata are known 
to occur is in Sindbad Valley, 12 miles south from West Creek. A 
fault running near the base of the northeastern scarp prevents a 
clear determination of the relations but the gypsiferous beds are 
manifestly older than the strata below the Dolores. ‘These belong 
no doubt in the series measured on West Creek. Owing to complex 
folding and faulting to be discussed on another page, the extent and 
relations of the gypsum-bearing beds cannot be ascertained, but they 
are apparently some hundreds of feet in thickness. 
That the gypsiferous section occurs between two series of sand- 
stones, shales, and conglomerates, is indicated by the observations 
on Grand River (p. 654). In discussing the unconformity at the 
base of the Dolores, it was stated that going northeast from Moab, up 
Grand River, a succession of shales, sandstones, and conglomerates 
appears between the fossiliferous Pennsylvanian beds and the Dolores. 
The structure brought out in Fig. 8 shows that the intermediate 
beds rest on the Pennsylvanian. 
At the time we traversed Grand River Valley, we did not know of 
the existence of the gypsiferous beds in that region, but on the way 
to the northern stope of the La Sal Mountains in the valley of Fisher 
Creek a considerable thickness of such strata was found. As in 
Sindbad Valley, a zone of faulting and folding interferes with an 
accurate determination of relationship on the line of travel. 
No doubt the detailed nature of the section between the Pennsyl- 
vanian and Triassic can be fully determined in Grand River Canyon, 
