514 EEPORT UNITED STATES GEOLOGICAL SURVEY. 



Besides the Green Eiver and Thompson Plateaus^ there are the Ham's 

 Eork Plateau and the Bear Lake Plateau, all of which will be hereafter 

 described in detail. 



Mountains. — The mountains of the district have in general the char- 

 acter of short, isolated ranges. The Bear Eiver Range, extending south 

 from the Great Bend of Bear Eiver, is the longest within our district 

 (having a length of 60 miles), and stretches some distance south of our 

 line to join the Wahsatch Range. The Wind Eiver Eange occupies a 

 small portion of our area in the northeast corner. 



On the west side of Green Eiver Basin are the Wyoming Mountains, 

 and west of them the Salt Eiver Eange. Although short, these are 

 important ranges. The Wyoming Eange ends at the head of La Barge 

 Creek, but the line of uplift is continued southward in the Absaroka 

 Eidges. The Salt Eiver and Wyoming Eanges both have north and 

 south trends. West of the Salt Eiver Eange we have no mountains until 

 we reach the Portneuf Eange. The northern end of the Preuss Eange, 

 it is true, extends northward between the east and south forks of the 

 Blackfoot, but the mountainous character is here nearly lost. Besides 

 this, there are only comparatively low ridges and isolated grouiDs of 

 hills in the northern part of the district between the Salt Eiver Eange 

 and the Portneuf Eange. West of the Portneuf is a range to which 

 we gave the name " Bannack." It extends southward, of very unequal 

 height, to the head of the Malade Valley. Opposite the southern end 

 of this range, at the head of Marsh Creek Valley, the Malade Eange 

 begins. This range consists really of two groups, the ends of which 

 overlap each other. The southern one ends just north of the " Gates " 

 of Bear Eiver, and on the south side, some distance from the river, is the 

 northern end of the Wahsatch Eange. A few degrees south of east 

 from the Portneuf Eange is a group of hills, some of which attain the 

 dignity of mountains. They are north of Cache Valley, lying between 

 Marsh Creek Valley and Bear Eiver. They will be described as the 

 southern extension of the Portneuf Eange. 



On both the eastern and western edges of the Bear Lake Plateau 

 erosion has removed the plateau character, and there are hills and ridges 

 with north and south trends. This is more noticeable toward the north- 

 ern end of the plateau. The hills on the east have been named the 

 Boundary Hills, as the boundary line separating Wyoming and Idaho 

 crosses them, following approximately their trend. 



Following the strike of the beds on the west side of the plateau, north- 

 ward across Bear Eiver, As^e find the ridges soon rising into a range, the 

 culminating peaks of which are found in Mount Preuss and the neigh- 

 boring mountains. Farther north the strike of the beds seems to turn 

 somewhat to the westward, and a number of ridges branch from the 

 range and are seen as spurs separating the branches of the Blackfoot 

 Eiver. 



North of Bear Eiver Valley is Sublette Eange, between Smith's Fork 

 and Thomas Fork. The strata composing these hills or mountains pass 

 under Bear Eiver Valley as we follow the strike southward. 



The western edge of the Ham's Fork Plateau is bordered b}- a line of hills 

 with a north and south trend. They stand on the east side of Eock 

 Creek and die out to the northward, where a second range, that marks 

 the west side of Eocli Creek, becomes the most prominent. The latter 

 range begins in a plateau-remnant in the angle of Twin and Eock Creeks, 

 and extends northward on the west side of Eock Creek and the east 

 side of Smith's Fork, until it loses the character of a distinct range in 

 the group of high mountains that connect the Salt Eiver Eange, the 



