86 ANNALS NEW YORK ACADEMY OF SCIENCES 



Page 



Silver Fork fault 139 



Minor faults 139 



Summary of conclusions 140 



Physiography 140 



Stratigraphy 141 



Structure 141 



Bibliography 142 



Physiography 142 



Stratigraphy and paleontology 142 



Structure 143 



Introduction 



The general geological features of the Wasatch Mountains have long 

 been known from the comprehensive reports of the early federal surveys. 

 Since these general studies were made, several special problems have 

 been investigated, with the result that many new facts have been added, 

 in the light of which, many of the first conceptions have been greatly 

 modified. 



One of the most important of these later observations is concerned 

 with the structure. The complicated tectonic features of this remarkable 

 range are only now beginning to be appreciated. The finding of large 

 overthrusts in the vicinity of Ogden by Blackwelder in 1909 and the 

 tracing of the great Bannock thrust from southern Idaho south into the 

 Wasatch range accomplished by Eichards and Mansfield of the U. S. 

 Geological Survey within the last year or two have added much impor- 

 tance to this phase of the structure. Boutwell had previously discovered 

 overthrusts in the Park City district, but they were thought to be local 

 features and were not greatly emphasized. 



As might be expected, the unravelling of the structure has had an im- 

 portant bearing upon the stratigraphy of the range, especially since the 

 regions in which the overthrusts have been found were those that fur- 

 nished the type sections to the early workers. The repetition of beds 

 brought about by overthrusting escaped the attention of the Fortieth 

 Parallel geologists, who gave the first unified account of the stratigraphy, 

 and their section is therefore subject to correction. 



It is the purpose of the writer to present in this paper a number of 

 facts that were observed in the summer of 1912 in the central part of 

 the Wasatch range, particularly in Big and Little Cottonwood Can3^ons, 

 and to discuss the structure and stratigraphy of that region. The dis- 

 covery of a great overthrust at Alta, in Little Cottonwood Canyon, has 



