F. GEOGRAPHY. 247 



one hundred and fifty miles, the east forming the divide be- 

 tween the Grand and the White. On the south side of the 

 crest are broken cliifs; on the north side, the branches of the 

 White caiion immediately. This leaves the divide in many 

 ]3laces very narrow, in some cases not more than thirty to 

 forty feet wide, with a vertical descent on the south toward 

 the Grand River, and an extremely steep earth slope (35 in 

 many cases) at the heads of the streams flowing north to the 

 White River. This crest, though not over 8500 feet in height, 

 is the highest land for a long distance in every direction. 



After leaving theUncompahgre Agency, the party followed 

 Gunnison's Salt Lake road to the Grand, and down that river 

 to the mouth of the Dolores, in latitude 38 50', longitude 

 109 17'. At this point they turned northward, and went up 

 to the crest of the Book Plateau. They followed this crest 

 to the eastward for upward of a hundred miles to longitude 

 108 15', and thence via the White River (Ute) Indian Agen- 

 cy to Rawlins, where they arrived on October 23d. 



The whole area worked is about 3500 square miles, in sur- 

 veying which about sixty stations were made. 



The geological work of this division, by Dr. Peale, connects 

 directly with that done by him in 1874 and 1875. Sediment- 

 ary formations prevail on both districts visited the past 

 season. 



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 caiions, 

 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 caiion, however, is no indication of 

 its importance as a stream-bed, for away from the main 

 streams they are dry the greater portion of the 3'^ear. There 

 are not great disturbances of the strata, what folds do occur 

 being broad and comparatively gentle. 



The San Miguel River, leaving the San Juan Mountains, 

 flows toward the northwest, and with its tributaries cuts 

 through the sandstones of the Dakota group, exposing the 

 variegated beds lying beneath, that have generally been re- 

 ferred to the Jurassic. About 25 or 30 miles north of Lone 

 Cone the river turns abruptly toward the west, and flows 



