18 G. K. Gilbert—The Colorado Plateau Province. 
they not only constitute some of the loftiest points, but are ex- 
ceptional to the general character of the topograph 
he climate is extremely dry—so dry that agriculture is 
impossible without irrigation. Vegetation is scant, except upon 
the heights. Below 8,000 feet altitude it is too sparse to inter- 
fere with the examinations of the geologist, and there are vast 
stretches of absolutely naked rock. Travel is greatly obstructed, 
except along certain lines, by deep cafions which ramify through ~ 
the plateaus, and the selection of routes for wagon-roads and — 
railroads is a work of great difficulty. : 
All this description applies more especially to the southern 
portions of the Ft i 
streams flow in shallower and broader valleys, and are more 
sluggish. The Green river, the main artery of drainage, is there 
less deeply sunken in the plain than in its lower course, and all 
erosion by running water Is hence less powerful. The profiles 
of the topography are more rounded, and accumulations of local 
drift and soil give rise to man’ ssy plains. 
he only important economic mineral of the whole region is 
coal, and this, though unlimited in quantity, is now utilized 
only where the Pacific railroad affords a market. Mines of the © 
precious metals are nearly unknown, and in default of these, 
Il, How the material is exposed for study. 
Asa field for the studies of the geologist, the Plateau province 
offers valuable matter in an advantageous manner. Let us be- 
gin with the consideration of the manner. 
First, the Climate. The air is so dry that, except on the heights | 
and at the margins of springs and streams, there is no turf, no 
accumulation of humus, often no soil, and so little vegetation 
that the view is not obstructed. From a commanding emi-— 
nence one may see spread before him, like a chart, to be read 
almost without effort, the structure of many miles of country, | 
and in a brief space of time may reach conclusions, which, in a — 
istrict. North of the Uinta mountains the ~ 
