78 Explorations in Colorado. [ February, 
The country first examined lies between the San Miguel and 
Dolores rivers, extending northward and northwestward from 
Lone Cone Mountain. The general character of this region is, 
that of a plateau cut by deep gorges or cañons, some of which, 
especially towards the north, extend from the sandstones of the 
Dakota Group to the top of the red beds. The depth of the 
caiions, however, is no indication of their importance as stream 
beds, for away from the main streams they are dry the greater 
portion of the year. There are no great disturbances of the 
strata, what folds do occur, being broad and comparatively gentle. 
The San Miguel River, leaving the San Juan Mountains, flows 
towards the northwest and with its tributaries cuts through the 
sandstones of the Dakota Group, exposing the variegated beds ly- 
ing beneath, that have generally been referred to the Jurassic. 
About twenty-five or thirty miles north of Lone Cone, the 
river turns abruptly to the west and flows west and southwest 
for about fifteen miles, when it again turns and flows generally 
northwest until it joins the Dolores. Between the San Miguel 
and Lone Cone the sandstones of the Dakota Group or number 
one Cretaceous are nearly horizontal, forming a plateau which on 
approaching the mountains has a capping of Cretaceous shales. 
Beyond the bend, the San Miguel flows in a monoclinal valley 
in which the cañon walls are of the same description as in the 
upper part of its course. As the mouth is approached the red 
beds appear. Between this portion of the course of the San 
Miguel and the almost parallel course of the Dolores, which is in 
a similar monoclinal rift, there are two anticlinal and two syn- 
clinal valleys parallel to each other. They are all occupied by 
branches of the Dolores. Lower Cretaceous Jurassic and Trias- 
sic strata outcrop and present some interesting geological details 
which will be fully considered in the report on the district. The 
Dolores River comes from a high plateau in a zigzag course, flow- 
ing sometimes with the strike and sometimes with the dip of the 
strata. Its general course on the western line is about northwest, 
from which it turns to the northward and westward, finally chang- 
ing to northwest again for its junction with the Grand. It is in a 
cañon the greater part of its course. 
In the region of country north of Grand River, the geological 
formations extend uninterruptedly from the red beds exposed on 
rand River to the white Tertiary cliffs forming the summit of 
the “ Roan Mountains” or Book Cliffs. The Grand is generally 
in a cañon in the red beds. 
