LETTER TO THE SECRETARY. 



Office United States Geological and 

 Geogeaphical Survey of the Territories, 



Washington^ D. C, October 1, 1875. 



Sir : I have the honor to present for publication the Annual Eeport of 

 the United States Geological and Geographical Survey of the Territories, 

 embracing a preliminary account of its operations in portions of Colo- 

 rado during the season of 1874. 



The headquarters of the survey in the field were made at Denver, as 

 in the preceding year, as the most suitable j)oiut for procuring the outfit 

 and making the necessary preparations for the various divisions which 

 were to investigate the districts specially assigned to them by the geol- 

 ogist-iu-charge. The entire survey was separated into wseven divisions. 

 Four were for regular topographical and geological duty, and were 

 assigned to specific areas ; one party for the primary triangulation ; a 

 photographic division, to which was attached a naturalist ; a party for 

 special topographical and geological study ; and the quartermaster's 

 division, that furnished all the parties above mentioned with supplies 

 during their field-work. 



The first division was composed as follows: — A. E. Marvine, assistant 

 geologist, director; S. B. Ladd, topographer; Louis Chauvenet, assistant 

 topographer ; M. L. Ward and W. S. Holman, meteorological observers; 

 E. A. Barber, botanist and collector; W. W. Williams, general assistant; 

 together with two packers, cook, and hunter. 



The party took the field on the 20th of July, crossing over Berthoud's 

 Pass, and through the Middle Park into the North Park, by the Willow 

 Creek Pass. The survey of the southern portion of this park employed 

 the party for some time; and it was not until the middle of August that 

 they crossed to the main field of their work west ojf the Park range. 



This new area presented all the different forms surface-erosion peculiar 

 to a granite, sedimentary, and lava country, making it an exceedingly 

 interesting study both for its topography and geology. The great 

 lava mesa situated at the head of the White River is cut by deep caQons 

 that penetrate far into the plateau, dividing the mesa into what appear 

 to be isolated masses, but which are all connected. One isthmus, from 

 three to twelve feet in width and one hundred and twenty-five in 

 length, connected a plateau, of several miles extent, with the main 

 mesa. The highest portion of this mass is on the east side, and, from 

 the base of the almost continuous cliffs which border it, the country 

 descends in long, timbered slopes to the broad, open area of Egeria 



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