' Hanging Valleys of Georgetown, Col. — Crosby. 47 
east side of this ridge is on a fault with the downthrow to the 
east, running straight up the north face of Leavenworth moun- 
tain, intersecting the oblique and east-west faults previously 
described and giving the northwestern angle of the mountain 
its salient character. The ridge just described, terminating in 
Hall's ledge, is clearly only a narrow remnant of the gradually 
tapering north end of Leavenworth mountain, which, we may 
or must believe, once separated the two creeks. Accepting this 
view, the displacement of the bed rock surface is probably not 
less than 100 feet; and the most anomalous feature is seen in 
the fact that the creek is left on the upthrow side for one-third 
of a mile after entering Georgetown basin. Sedimentation in 
this basin has virtually obliterated the fault as a topographic 
feature of the valley floor and destroyed the water power to 
which it gave rise. Were the valley 'cleared of detritus, the part 
of the valley of Clear creek' above the fault would become a 
hanging valley in its relation to the Georgetown basin, or gra- 
ben, or that part of the valley below the fault. 
Under existing conditions, however, and in spite of the ac- 
cumulated detritus below the main fault just described, the 
floor of this valley is abnormally elevated for a short distance, 
where it is trenched by the gorge, some seventy-five feet in 
depth, known as the Devil's Gate (Figure 3). The part of the 
valley above the Devil's Gate, which may conveniently be des- 
ignated the Silver Plume valley, is, aside from the morainal 
deposits which terminate half a mile or more above the Devil's 
Gate, flat-bottomed and free from a gorge down to the begin- 
ning of the Devil's Gate, where the rocky floor is abruptly up- 
lifted at least seventy-five feet. In other words, local move- 
ment, or block faulting between two of the fractures crossing 
the northern face of Leavenworth mountain, has raised a rock 
dam across the valley here approximately seventy-five feet high 
and 500 to 800 feet broad up and down the valley. Through 
this dam the stream has cut its gorge ; and the absence immedi- 
ately above this barrier of stratified deposits or any evidence of 
a lake is a plain indication that the elevation was gradual, and 
so slow that the stream kept pace with the movement. The 
former course of Clear creek across this elevated tract can be 
traced along the line of the railroad east of the gorge in the 
waterworn ledges and pot-holes and well-rcunded and vvater- 
