THE HART MOUNTAIN OVERTHRUST 49 
This escarpment is a very striking feature of the scenery along 
the Cody Road to Yellowstone Park, just west of the Shoshone 
Reservoir. 
Traced westward up the valley the fault on either side passes 
beneath the Tertiary volcanics and is lost. It passes in a bold 
escarpment around the east end of the divide between the North 
and South forks of Shoshone River and extends for several miles 
up the north side of the latter valley, where it is again buried 
beneath the Tertiary breccias. It does not reappear on the south 
side of the valley of the South Fork except as an isolated peak of 
Madison resting on Fort Union(?) at the east end of Carter Moun- 
tain in Sec. 36, T. 51 N., R. 103 W. Several miles south of this 
point, however, abundant Madison bowlders are noted along the 
slopes on the east and southeast of Carter Mountain, indicating 
that the fault block of Madison probably occurs buried beneath 
the lavas of that mountain, or even possibly outcropping in small 
overlooked exposures along the lava scarp of that divide. 
On the north side of the North Fork Valley the scarp makes a 
sharp re-entrant where Trout Creek cuts through the faulted 
block. In Sec. 6, T. 52 N., R. 103 W., the scarp bends abruptly 
northwestward and extends for a long distance along the west side 
of Rattlesnake valley, overlapped at several points by Tertiary 
volcanics, beneath which it passes at the head of the valley. In 
this distance the Madison rests on successively older beds, from 
Cody shale to Chugwater “‘Red Beds.” The trace of the fault could 
not be found on the east side of Rattlesnake valley, from which the 
block of faulted Madison has probably been largely removed by 
_later erosion. It is suspected that fragments of the block still 
remain on the top of Rattlesnake Mountain anticline, but if so they 
probably rest, Madison on Madison, and have not been detected. 
Along the divide between Rattlesnake valley, Pat O’Harra valley, 
and Dead Indian valley the trace of the fault plane could not be 
found, either because wholly removed by erosion or because Madi- 
son was faulted on Madison and not detected. In Sec. 3, T. 54N., 
R. 104 W., the fault plane again emerges from beneath a small 
patch of Tertiary breccia and traces easily northwestward, to the 
point where the wagon road crosses Dead Indian Ridge, a distance 
