THE BANNOCK OVERTHRUST 
westernmost observed portion of the 
fault trace in Georgetown Canyon 
and the easternmost portion of that 
trace in Crow Creek is about 12 
miles. It appears, therefore, that 
the heave may be equal at least to 
that distance. 
In the ridge west of Slug Creek 
(Fig. 2) an elongate area apparently 
surrounded by a fault boundary is 
interpreted as an anticlinal portion 
of the main thrust, or of a subordi- 
nate thrust, unroofed by erosion so 
that the underlying block is exposed 
through a ‘‘window”’ or ‘‘fenster.”’ 
The position of this window with 
reference to the anticline in the north 
fork of Georgetown Canyon is favor- 
able to this interpretation. 
JOHN GRAYS LAKE AND BLACKFOOT FAULTS 
Reconnaissance by the senior 
author and Dr. A. R. Schultz of the 
U.S. Geological Survey northward 
from the area above described and 
in the vicinity of John Grays Lake 
developed the presence of a thrust 
fault of similar magnitude in that 
region. While this fault has not 
been traced directly into the George- 
town fault, from the position of the 
thrust and its general relations it is 
interpreted as a continuation of that 
fault. The northwestward extension 
of the John Grays Lake fault is con- 
cealed by flows of basalt. A similar 
thrust was recognized in the same 
reconnaissance in the Blackfoot 
Range. The alignment and _ the 
Fic. 3.—Panorama from south-pointing spur on hill north of Georgetown Canyon (see Fig. 2) looking northeast to nearly due south. Meade 
Peak is situated to the left of the middle of the picture. 
The trace of the Bannock thrust and a sharp drag fold in the overthrust Mississippian 
limestone is shown in the left foreground. The trace of the Bannock fault is also indicated on the divides between Georgetown and South 
Canyons, the latter and Dunn’s Canyon; thence to the head of the latter where it crosses to the head of Montpelier Creek where it appears: 
in Fig. 4. For explanation of letter symbols, see Fig. 1. - 
OV 
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9 
