REPORT ON THE GEOLOGY OF THE GREEN RIVER DISTRICT. 



By Dr. A. C. Peale. 



CHAPTER I. 

 GENEBAL INTEODTTCTION. 



AREA. 



The district assigned the Green Eiver Division for the season of 1877 

 lies "between the meridians 109° 30' and 112° and between the parallels 

 41° 45' and 43°. This includes an area of about 11,100 square miles, the 

 larger portion of which lies within the limits of Wyoming Territory, the 

 rest being divided between Utah and Idaho. The area thus indicated 

 was surveyed, and in addition to it a belt of country reaching west to 

 meridian 112° 30', so that the entire area surveyed amounts to 13,000 

 square miles, distributed among the three Territories as follows : 



Square miles. 



"Wyoming 6, 562 



Idaho 5,328 



Utah 1,110 



Total 13,000 



On the east our work connected directly with that of the Sweetwater 

 Division, under Mr. Chittenden and Dr. Endlich. Our northern line 

 was the southern limit of the work of the Teton or Snake Eiver Division^ 

 under Mr. Bechler and Mr. St. John. The country bordering our dis- 

 trict on the south has been explored and mapped in detail by the Survey 

 of the Fortieth Parallel, under the direction of Clarence King. 



FORItfER GEOLOGICAL EXPLORATION. 



Although from the time of Bonneville's explorations to the present time 

 the district has been traversed by many parties, little has been added to 

 our knowledge of the country outside of their immediate routes of travel. 

 This refers more particularly to the eastern and northern portions, for 

 the western and southwestern parts of the district are comparatively well 

 settled and therefore well known. Nearly all previous explorations were 

 for the specific purpose of selecting routes for wagon-roads across the 

 country, and the additions made to our knowledge were geographical 

 and to a limited degree topographical rather than geological. This sub- 

 ject will, however, be referred to in more detail by Mr. Gannett in his 

 report. The only geological explorations previously carried on in the 

 district were of a reconnaissance character, and extended over but limited 

 portions of the district. The explorations of the Geological Survey in 

 in 1870, 1871, and 1872, comprises the largest portion of this reconnais- 

 sance work. 



In 1870 Dr. Hayden passed near our eastern line on his way from 

 South Pass to Fort Bridger, following down the Little and Big Sandy 

 Eivers.* 



* Report U. S. Geol. Surv. of Ter. for 1870, 1871, pp. 39-41. 



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