1877 -] 
Prof. Hayden's Explorations. 
243 
and went up to the crest of the Book plateau. They fol- 
lowed the crest to the eastward for upward of a hundred 
miles, or to longitude 108° 15' ; then descended to the Grand, 
and followed it up to longitude 107° 35', and thence via the 
White River (Ute) Indian agency, to Rawlins, where they 
arrived on October 23rd. 
The whole area worked is about 3500 square miles, in 
surveying which about sixty stations were made. 
The geological work of this division, by Dr. Peale, con- 
nects direCtly with that done by him in 1874 an< ^ 1875. 
Sedimentary formations prevail on both districts visited 
during the past season. 
The country first examined lies between the San Miguel 
and Dolores Rivers, extending northward and north-west- 
ward from Lone Cone Mountain. The general character of 
this region is that of a plateau cut by deep gorges or canons, 
some of which, especially toward the north, extend from 
the sandstones of the Dakota group to the top of the Red 
Beds. The depth of the canon, however, is no indication 
of its importance as a stream-bed, for, excepting the main 
streams, they are dry the greater portion of the year. 
There are not great disturbances of the strata, what folds 
do occur being broad and comparatively gentle. 
The San Miguel River, on leaving the San Juan moun- 
tains, flows toward the north-west, and, with its tributaries, 
cuts through the sandstones of the Dakota group, exposing 
the variegated beds lying beneath, that have generally been 
referred to the Jurassic. About 25 or 30 miles north of 
Lone Cone, the river turns abruptly to the west, and flows 
west and south-west for about 15 miles, when it again turns 
and flows generally north-west, until it joins the Dolores. 
Between the San Miguel and Lone Cone the sandstones of 
the Dakota group, or No. 1 cretaceous, are nearly horizon- 
tal, forming a plateau which, on approaching the mountains, 
has a copping of cretaceous shales. 
Beyond the bend the San Miguel flows in a monoclinal 
valley, in which the canon walls are of the same description 
as in the upper part of its course. As the mouth is ap- 
proached the Red Beds appear. Between this portion of 
the couise 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 synclinal valleys parallel to each 
other. They are all occupied by branches of the Dolores 
lower cretaceous, jurassic, and triassic strata outcrop, and 
present some interesting geological details, which will be 
fully considered in the report on the District. The Dolores 
