DAVIS: THE PLATEAU PROVINCE OF UTAH AND ARIZONA. 15 
valley on its southwestern side ; and it is this local bending of the sand- 
stones that produces the monoclinal flexure of Pipe spring. The sand- 
stones on the further side of Moccasin valley are horizontal close to the 
main Sevier fault, except for the gentle northward dip that prevails 
through the whole region. 
The floor of Moccasin valley —see Plate 3 A—is broadly covered 
with wash, but near its northeastern side the weak blue clays of the 
lower Trias are seen near the base of the enclosing escarpment. It is 
therefore concluded that the valley is underlaid by these weak beds, 
whose easy removal has caused the retreat of the Trias to the northeast. 
A branch fault must be here inferred, curving northwestward from the 
main fault along the southwestern side of Moccasin valley with a heave 
of twelve hundred feet or more on the northeast. The further end of 
the fault did not seem more than five or six miles away to the north- 
west, but it was not traced. 
t 1000 Fr. 
Ficore 5. 
Diagram of the unconformity at the base of the Shinarump. 
Moccasin spring, like Pipe spring, supplies water enough for a small 
ranch. The two springs are about three miles apart; they are alike in 
flowing out at the eastern base of the sandstone monocline, where these 
permeable strata are faulted against impermeable clays; Triassic clays in 
the first case, Permian clays in the second. 
Erosion iN THE PireE Serine District. —The abundant erosion in 
the Pipe spring district since the production of the Sevier fault has had 
three characteristic but different effects, each controlled by the structure. 
First, all the outcrops of corresponding strata on the two sides of the 
fault are out of line by ten or twelve miles ; this distance measuring the 
excess of escarpment-retreat in the uplifted eastern block over that in 
the western block, as has been pointed out. Second, where weak 
members of different horizons are brought together on opposite sides of 
the fault, the land surface is worn down to a relative lowland of even 
grade across the fault line; that is, the fault is there topographically 
extinguished. This is well shown just south of Pipe spring, where the 
lowland of the Triassic clays west of the fault line is drained to the low- 
