610 ALLEN DAVID HOLE 
direction. Between these ridges the surface of the deposit is 
uneven, hummocky, and including kettles occupied in part by small 
ponds. But although the topography is irregular and uneven, yet 
the longer dimensions of both the kettles and the elevations are in 
general parallel to the ridges. The material of the drift on this 
mesa includes a variety of rocks such as are common to the region; 
striated bowlders occur at numerous points. The ridges trending 
northeast-southwest are believed to be due primarily to the action 
of ice which occupied the valley of Lake Fork; that is, they repre- 
sent successive positions of the edge of the Lake Fork Glacier as it 
was finally withdrawing from the mesa, and are, therefore, to be 
classed as recessional moraines. The north-south ridge near the 
northern end of the mesa, with its steep western slope, indicates 
that it, too, was deposited by a glacial sheet from the east. South- 
ward from the lowest part of the mesa as referred to above, the 
topography is uneven, and not marked by distinct ridges except 
for a prominent medial moraine three-fourths of a mile long extend- 
ing from the point of junction of the Bilk Creek and Lake Fork 
glaciers down to an elevation of about 9,400 feet. 
East of Lake Fork, between the San Miguel River and Turkey 
Creek, the surface of the drift is more or less rough or ridged, the 
dominant trend of these ridges being parallel to the valley of Lake 
Fork. The most prominent ridge extends from Vance Creek to 
Turkey Creek near the eastern edge of the drift, reaching an 
elevation of more than 9,500 feet at its highest point. North of 
Vance Creek, while the irregularities of the surface of the drift 
show distinctly linear arrangement, the ridges are neither so 
prominent nor so persistent as on the mesa west of Lake Fork. 
Southward from Turkey Creek on the east side of the valley for 
more than two and one-half miles, the topography is wholly irregular 
and confused. The change in arrangement of the drift is partly » 
due to the greater steepness of the slope on which it lies. From 
the San Miguel valley to Turkey Creek on the east side of Lake 
Fork, sedimentary rocks outcrop along the east wall of the valley 
in a precipitous face below the comparatively level drift-covered 
area above; but south from Turkey Creek, the sedimentary series 
