34 GEOLOGY OF THE HIGH PLATEAUS. 



south of Salina. Resuming its northerly trend, the fault with a reversed 

 throw passes along the west side of Gunnison Valley with a shear of at 

 least 3,000 feet, and runs obliquely up on the great Wasatch Monoclinal, 

 forming a superimposed displacement, and then cuts obliquely down into 

 San Pete Valley, where it disappears. It may continue farther northward, 

 but it has not been traced in that direction beyond San Pete Valley. Its 

 total observed length is very nearly 100 miles. It is everywhere a true 

 fault, though at several places it is complicated by minor fractures and some 

 flexing of the thrown beds. 



I have not included the East Miisinia fault among the greater displace- 

 ments, though it has considerable length — perhaps 45 miles — and at one 

 j^lace in Gunnison Valley the shear reaches more than 2,000 feet, and pos- 

 sibly near to 3,00!' feet. It is, however, an important feature, and almost 

 entitled to rank with the greater faults of the system. It is parallel to the 

 northern portion of the Thousand Lake fault last described, and might be 

 called a mate to it, since the two hold between them the sunken block of 

 Gunnison Valley and the continuation of that block obliquely across the 

 great Wasatch Monoclinal. 



This sunken block is an interesting occurrence, and belongs to that 

 kind of complicated fracture which Powell has named "Zone of Diverse 

 Disjilacement." The part of it which lies in the lowest portion of Gunnison 

 Valley has been analyzed and described by Mr. Gilbert. It extends both 

 north and south from this locality, and in the former direction continues to 

 display the same comminuted fracture in great variety for a distance of 

 more than 20 miles, while the width of the zone does not exceed 3 miles. 

 It appears to be a veiy clear case of a block dropping through the drawing 

 apart of the strata and sinking to fill the gap thus produced. Another in- 

 stance occurs along the western base of the Aquarius Plateau in the south- 

 ernmost portion of Grass Valley. Here the block between the faults, 

 instead of shearing shai'ply on both sides, has partly careened and settled 

 down synclinally. 



These displacements do not belong wholly to any one period. There 

 is evidence that different faults belong to different ages — not widely separ- 

 ated probably, but recognizably distinct. There is evidence that different 



