644 WHITMAN CROSS 
As far as I am aware no geologist has described the wonderland 
lying between Grand River and the Cretaceous divide between the 
La Sal and Abajo Mountains since the vivid pen pictures of New- 
berry in his report of the Macomb expedition (28). Nor can one 
easily equal the clearness with which the broader features of this 
fascinating region are portrayed. To one familiar with the formations 
Newberry’s descriptions are for the most part easily interpreted. 
Descending from the Great Sage Plain, with its Dakota floor, one 
passes first some 500-600 feet over the steep slope where the soft sand- 
stones and red or green shales of the McElmo occur, but are seldom 
well exposed. Below them is the upper sandstone of the La Plata, 
about 300 feet in thickness, which forms low mesas or ridges between 
the branches of Dry Valley, the main floor of which, over wide stretches, 
is near the upper surface of the lower La Plata sandstone. The 
upper member is a fine and even-grained massive sandstone, strongly 
cross-bedded, of yellowish or pinkish color, and lends itself to a very 
characteristic sculpturing. We fell at once into the habit of calling 
this member of the La Plata in Dry Valley the alcove sandstone, 
from the numerous recesses exhibited in nearly all its cliff exposures. 
Newberry illustrates this feature of a hill called by him ‘Casa Colo- 
rado,” and in the files of the Geological Survey is a photograph by 
W. H. Jackson, clearly of the same subject, reproduced here as 
Mga : 
Certain remnants of the alcove sandstone now standing as isolated 
hills are very striking. One of these, known as Looking-glass Rock, 
is situated southwest of the La Sal Mountains near and east of the 
road from Monticello to Moab. It is represented in Fig. 2. Another 
remnant of erosion is shown in Fig. 3. Near the base of this knoll 
a band of marked red color transgresses the stratification very mark- 
edly, serving to show the secondary origin of the red color in this case. 
The massive character of the upper La Plata sandstone is further 
illustrated by Fig. 4, representing the cliffs of the upper La Plata in 
the canyon of Grand River a few miles above the Moab ferry. The 
incipient alcoves at this point seem largely due to jointing. 
The middle calcareous member of the La Plata is apparently 
represented in Dry Valley by less than 100 feet of thinly-bedded 
strata, sandstones for the most part, with shaly and impure cal- 
