162 GEOLOGY OF THE HIGH PLATEAUS. 



mainly to erosion, the degradation of 1,500 to 2,000 feet of beds having 

 proceeded unequally, although the stratification still retains its sensible 

 horizontality. Upon the southwestern shoulder there is considerable com- 

 plication of the displacement. Two or three sharp faults, running north 

 and south, include between them a long block from 2 to 3 miles in width, 

 which has dropped, the amount of the fall varying from 600 to 1,700 

 feet. The length of this block is at least 27 miles and may be greater. 

 It is much complicated by minor fractures, and a portion of its southern 

 extension into the Cretaceous terrace south of the Wasatch Plateau has 

 been described and illustrated by Mr. Gr. K. Gilbert* as an instance of a 

 "zone of diverse displacement." The general appearance and relations of 

 this complicated downthrow suggest that the upper recurving branch of the 

 great monoclinal was subject to tension during the uplift, and the beds, 

 being unable to stretch, were rent apart, allowing the block to sink. 



The Cretaceous terrace, upon which we may look down while standing 

 upon the southern terminus of the Wasatch Plateau, is no doubt, from a 

 structural point of view, a part of that plateau; but the loss of its Tertiary 

 beds by erosion has reduced its altitude to a level 1,500 to 2,000 feet lower. 

 It continues the structural features soutliward to plateaus next in order, 

 forminjj a kind of connecting-link between the northern and southern 

 uplifts. Its chief deformation is due to the sunken block already described. 

 The two faults between which it has fallen increase for a time their throw 

 as they contiiuie southward, reaching a maximum of nearly 3,000 feet, and 

 then decreasing to zero at points about 18 and 20 miles, respectively, south 

 of the Wasatch Plateau. The structural depression thus produced has been 

 called Gunnisoa Valley, but, this name being preoccupied, it should be used 

 provisionally. It contains abundant evidence of its origin, for the Tertiary 

 beds are seen to abut against the Cretaceous along the lines of faulting, 

 and the latter beds tower far above them. The drainage of this valley is 

 to the westward, thi'ough a deep canon called Salina Caiion, which is a 

 clearly defined, but by no means uncommon example of a general fact, 

 which is repeated so frequently throughout the entire Plateau Country that 



*Amer. Jour. Science; also, Geol. 'Uinta Mountains, J. W. Powell. The minor IVactures are too 

 small to appear effectively upon the stereogram, and have been omitted, but the main faults are intro- 

 duced. 



