LETTER TO THE SECRETARY. 9 



the appearance of long hog-backs. On the south side, the plateau pre- 

 serves its horizon tali ty for a few miles, then breaks oft, leaving a ridge 

 of upturned beds only to separate the river from the valley of the 

 Uncompabgre. At a point about thirty miles below the head of the 

 canon, the river changes its course abruptly from west to north, and 

 flows parallel to the slope of long hog-backs. It holds this course for 

 about eighteen miles, then, at the mouth of the North Fork, a large 

 affluent from the north, it turns again abruptly to the west, and a few 

 miles farther suddenly emerges from the canon into the broad valley of the 

 Uncompabgre. The character of this canon in its upper part is extremely 

 rugged ; its walls are precipitous, and there is hardly a place where a 

 man could clamber down to the bottom. The river fills the bottom of 

 the canon, leaving no beach anywhere. The material of the canon- 

 walls in the upper two-thirds is gneiss and in the lower third stratified 

 rock. The valley of the Uncompahgre Eiver is very broad, extending 

 forty miles up the Uncompahgre Eiver and twenty miles down the 

 Gunnison. Below this, the river falls through a canon, which, with 

 slight interruptions, extends to the mouth of the river, while the country 

 back from the river is a flat open valley. 



The Elk Mountains extend into this district, occupying an area of 

 about one thousand five hundred square miles in the southwestern 

 part. Their character is not that of a continuous range, but of groups 

 of mountains and isolated peaks. The elevation of the highest does not 

 exceed 13,500 feet, and the average of the peaks is scarcely 13,000 feet. 

 These mountains are drained entirely by the Gunnison ; the northern 

 slopes by its North Fork. Besides these mountains, the country is 

 entirely plateau and broad valleys. The plateau has an elevation of 

 8,500 to 10,000 feet, sloping gradually toward the west. The elevation 

 of the mouth of the Gunnison Eiver is about 4,200 feet ; at the mouth 

 of the Uncompahgre, 4,500 ; and the general elevation of the Uncom- 

 pahgre Valley, 4,500 to 5,000 feet ; that of the mouth of Cochetopa 

 Creek, 7,400 feet ; and of the Grand Eiver, at the mouth of the Eagle, 

 about 7,000 feet. 



The division was constituted as follows, viz: Henry Gannett, topog- 

 rapher, in charge of party ; Dr. A. C. Peale, geologist ; Fred. Owens, 

 assistant topographer; Frank Kellogg, assistant; Arch. E. Balloch, 

 general assistant ; with two packers and a cook. 



The party left Denver on July 21, traveled one hundred and fifty 

 miles to their field of work, commenced work August 3, ended work 

 October 29, and reached Denver about the middle of November. 



On July 14, 1874, the San Juan or third division of the United States 

 Geological and Geographical Survey left Denver for the field. Itconsisted 

 of A. D. Wilson, topographer, directing; F. Ehoda, his assistant; F. M. 

 Endlich, geologist; and Mr. Gallup, who was for a short time attached 

 as barometric observer. The region assigned to this division was the 

 one generally known as the " San Juan country". In I860 and 1861,. a 



