700 R. W. RICHARDS AND G. R. MANSFIELD 
effects of the two are practically identical and Uy clearly may 
represent the same crustal break. 
MONTPELIER FAULT 
The work of Gale and Girty in 1909 (10e) in the Montpelier 
district demonstrated the existence near Montpelier of a great 
thrust fault in which heavy Mississippian limestones from the west 
were overthrust upon Lower Triassic formations, the Woodside, 
Thaynes, and Ankareh. Northward, southward, and westward 
the fault trace passes beneath the cover of late deposits. To the 
south no further indication of thrust faulting has been recognized 
on the east side of Bear Lake Valley, though a normal fault of 
considerable importance lies along the east shore of Bear Lake. 
To the north, however, at no great distance lies the Georgetown 
thrust fault, in which the structural relations of older and younger 
rocks are closely similar to those of the Montpelier district. There 
seems therefore good reason for the supposition that the two 
faults are continuous beneath the covering of alluvium and Tertiary 
deposits. 
SWAN LAKE FAULT 
In 1910 the writers found a thrust fault along the west base 
of the Aspen Range east of Bear Lake Valley, particularly well 
developed near Swan Lake, about 7 miles southeast of Soda Springs 
(Fig. 1). Here similar conditions hold and Carboniferous lime- 
stones lie upon Triassic rocks. The dip of the fault plane here 
appears to be eastward but this feature may, as in the Georgetown 
block, be due to deformation of the fault plane, for the source of 
the older rocks appears to be to the west as in the Georgetown 
fault. The trace of the Swan Lake fault ig marked by the occur- 
rence of sulphur and calcareous springs and also by great deposits 
of travertine, of which Formation Spring, 3 miles northeast of Soda 
Springs, with its basins and terraces is a beautiful example. In the 
1910 report (1of) it was argued that these springs marked the trace 
of a normal fault that cut the Carboniferous thrust block along the 
west base of the Aspen Range. In the light of the later studies 
in the Georgetown region it seems probable that all the features 
ascribed to the normal fault can be better explained by the deforma- 
