68 APPENDIX TO THE REPORT OF THE SECRETARY. 



Range and the contiuental water-slied north to Togwotee Pass, the Gros 

 Ventre Mountains southeast of Jackson's Basin, and in the southwest 

 the considerable area south of the Grand Canon of the Snake filled by 

 the southern i)rolongation of the Snake River Mountains, or what is 

 here known as the Wyoming- Range, in which latter quarter the work 

 commenced. 



The approach was from the soutb up the valley of Green River, which 

 forms a considerable basin area in the southern central portion of the 

 district, and which is entirely filled with deposits of the age of the Ter- 

 tiary. These decline basin wards on the three sides hemmed by the Wy- 

 oming, Gros Ventre, and Wind River Mountains, attaining a thickness 

 of several thousand feet. 



The northern end of the Wyoming Range was here found to consist 

 of several quite well defined low ridges which reach the maximum of 

 ruggedness in the Carboniferous barrier ridge on the western border 

 along Salt River. To the east of this belt Hoback's River rises in a basin 

 area south of the Gros Ventre Range, which, geologically, is part of the 

 Green River Basin, the water-divide being merely a low ridge composed 

 of the soft arenaceous Tertiary beds. The latter are here unconformably 

 uplifted on the border of the Hoback Caiion ridge, the easternmost of 

 the Wyoming Range, and which is made up of Carboniferous and Meso- 

 zoic formations occupying a synclinal, either border of which apprars 

 iu the monoclinal crests on the east and west sides of this ridge. 



A tributary of the Hoback on the w^est of the canon ridge flows 

 through a valley which penetrates southwards nearly to the southern 

 border of the district. In this vicinity the western crest of the Hoback 

 Canon ridge shows an anticlinal structure, the Carboniferouson the west 

 flank being succeeded by the Trias, Jura, and Cretaceous, and finally a 

 heavy series of sandstones and variegated arenaceous shales which prob- 

 ably pertain to the Laramie. The latter stretch across the valley, (lip- 

 ping westwardly, and impinge on the next west-lying mountain ridge, 

 which is also composed of Carboniferous strata, abruptlj^ tilted and 

 faulted, with downthrow on the east. Inclining off the west slope of 

 this ridge the same series of geological formations are met with as men- 

 tioned abov^e, the later-formed showing subor<linate folds and making up 

 the bulk of the highland to the west which has been carved into a ^ery 

 broken belt by the erosion of the eastern tributaries of John Gray's 

 River and the gorges descending to the Snake. lU'yond tliis nearly the 

 same stratigraphic;il and structural features r(^cur in tlie more bulliy 

 ridge which occu])ies the interval extending over to Salt River, viz, 

 westerly dipping Mesozoic and Post-Cretaceous deposits, in!])inging 

 against the faulted Carboniferous in the ridge <»n tiie west. 



In the latter region much information was gained relative to the 

 identity in stratigraphical and structural elements that subsist here and 

 in the cluster of mountains culminating in Mount Baird north of the 

 Grand Canon. The whoh^ region here referred to proved to be exceed- 



