FORT HALL INDIAN RESERVATION 265 



siderable areas which intervene have not yet been mapped, and in the 

 mapped areas the older rocks and structures are largely concealed by 

 younger sediments and by igneous rock. Tensional faulting of later date 

 has also been recognized and described. These structural features are 

 all illustrated in the geologic map and structure sections that accompany 

 the report cited. 



Area of seven Quadrangles 



Seven quadrangles in the vicinity of the Wyoming border have been 

 studied rather intensively. These include the Montpelier 30-minute 

 quadrangle at the south and six 15-minute quadrangles, namely, the Slug 

 Creek, Crow Creek, Lanes Creek, Freedom, Henr}^ and Cranes Flat 

 quadrangles. Together they occupy parts of Bingham, Bonneville, Cari- 

 bou, and Bear Lake counties and comprise an area of about 2,000 square 

 miles. Preliminary accounts of some of the structural features of this 

 area have already appeared in connection with official reports or in special 

 papers,^ to which the reader is referred for available details. A compre- 

 hensive report covering the entire area has been prepared for publication 

 as a professional paper of the United States Geological Survey. 



The area contains a number of mountain ranges, members of the 

 Idaho-Wyoming chain, that have been complexly folded and faulted, and 

 the folds show a pronounced curvature in trend from a direction a little 

 east of north in the Montpelier quadrangle to northwest in the more 

 northerly quadrangles. Some of the folds exceed 50 miles in length and 

 3 miles in breadth, the more important being synclinoria with relatively 

 narrower intervening anticlines or anticlinoria. Usually they are uns3^m- 

 metrical and inclined or even overturned eastward or northeastward. 

 The axes for long distances are nearly horizontal or slightly undulatory, 

 due to the presence of relatively broad and low transverse folds, and the 

 pitch is gentle, generally toward the north or northwest. 



In the last paper cited above the writer has given descriptions of the 



3 H. S. Gale and R. W. Richards : Preliminary report on the phosphate deposits In 

 southeastern Idaho and adjacent parts of Wyoming and Utah. U. S. Geol. Survey Bull. 

 430, 1910, pp. 457-535. 



R. W. Richards and G. R. Mansfield : Preliminary report on a portion of the Idaho 

 phosphate reserve. U. S. Geol. Survey Bull. 470, 1911, pp. 371-451. 



R. W. Richards and G. R. Mansfield : Geology of the phosphate deposits northeast 

 of Georgetown, Idaho. U, S. Geol. Survey Bull. 577, 1914. 



R. W. Richards and G. R. Mansfield : The Bannock overthrust, a major fault in 

 southeastern Idaho and northeastern Utah. Jour. Geol., vol. 20, 1912, pp. 681-707. 



G. R. Mansfield : Igneous geology of southeastern Idaho. Bull. Geol. Soc. America, 

 vol, 32, 1921, pp. 249-266. 



G. R, Mansfield : Types of Rocky Mountain structure in southeastern Idaho. Jour. 

 Geol., vol. 29, 1921, pp. 444-468. 



