LETTER TO THE SECRETARY. 



Office U. S. Geological and 

 geoaraphical survey of the territories, 



Washington, January, 1878. 



Sir : I have the honor to transmit for publication the tenth annual 

 report of the geological and geographical survey under my direction^ 

 embracing the completion of the work known as the survey of Colorado 

 and portions of adjacent Territories. The systematic field investigation 

 of the six rectangles which are included in what is called the Atlas of 

 Colorado was commenced in the spring of 1873, and closed with the 

 season of 1876. These six sheets embrace an area of rugged mountainous 

 country of about 70,000 square miles. The field-work of the season of 

 of 1876 was therefore entirely confined to the completion of the work in 

 Colorado, and thus the area under investigation was located in the 

 interior of the country, far remote from settlements, and among hostile 

 bands of Ute Indians that attacked three of the parties the previous year. 



The point of departure the past season was Cheyenne, Wyo. Two 

 of the parties, with all their outfit, were transported by railroad to 

 Eawlins Springs, and proceeded thence southward. The other two 

 were sent by railroad from Cheyenne southward, one party to Trinidad 

 and the other to Caiion City. 



The primary triangulation party was placed in charge of A. T>. Wil- 

 son, and took the field from Trinidad, the southern terminus of the 

 Denver and Eio Grande Eailroad, August 18, making the first station 

 on Fisher's Peak. From this point the party marched by the valley of 

 the Purgatoire, crossed the Sangre de Cristo range by way of Costilla 

 Pass, followed the west base of the range northward as far as Fort Gar- 

 land, making a station on Culebra Peak. 



About six miles north of Fort Garland is located one of the highest 

 and most ragged mountain -peaks in the West, called Elanca Peak, the 

 principal summit of the Sierra Blanca group. On the morning of 

 August 28, the party, with a pack-mule to transport the large theod- 

 olite, followed up a long spur which juts out to the south. They found 

 no difficulty in riding to timber line, which is here about 12,000 feet 

 above sea-level. At this point they were compelled to leave the ani- 

 mals, and, distributing the instruments among the different members 

 of the party, proceeded on foot up the loose, rocky slope to the first 

 outstanding point, from which a view could be obtained of the main 

 peak of the range. Although this first point is only 600 feet lower than 

 the main summit, yet the most arduous portion of the task was to come. 

 The main summit is about two miles north of the first point, in a straight 

 line, and connected with it by a very sharp-toothed, zigzag ridge, over 

 which it is most difficult to travel, on account of the very loose rocks 



