564 



PROCEEDINGS OF THE ALBUQUERQUE MEETING 



them partly or wholly ire-covered. One of the most beautiful examples is 

 shown in plate 35, figure 2. 



Other lakelets or moist hollows occur among the morainic deposits in the 

 lower canyons or on the foot slopes of the mountains, particularly in the vicin- 

 ity of Sweetgrass and American Fork creeks. A steep-sided lake of this kind 

 near Swamp creek was estimated to be one-fourth of a mile in length. 



The largest lake in the Crazy mountains, known as Cottonwood (Forest) 

 lake, in the northern section, owes its being to an obstruction of loose porphy- 

 ritic blocks, that is probably morainic, though other signs of glaclation in the 

 valley in which it occurs are not very distinct. The linear form and fairly 

 regular outline of the lake are favorable to this view, though the valley is not 

 very trough-like in character, has no cirques at its head or along its sides, and 

 has no other well defined morainic deposits. 



The alternative view that the obstruction is simply a pile of fragments of a 

 hard dike or sheet weathered in situ is not supported by evidence of the con- 

 tinuation of such dike or sheet on the sides of the valley. The porphyritic 

 masses appear to be all of the same kind, but might have come from similar 

 rocks up valley. 



Relations to Previous Topography 



peneplanation 



Reference has been made to the gentle outlines of the upper topography of 

 the northern section of the mountains. Loco mountain, the main massif of 

 that region, has a nearly flat top .3 or 4 miles long and 1 or 2 miles wide at an 

 altitude of 9,000 feet. A small knoll rising 200 feet above the general level 

 forms Loco peak, the highest summit. The gentle outlines here mentioned 

 have been produced upon both sedimentary and igneous rocks, regardless of 

 structure, and represent an ancient surface of ei'osion. This is now deeply 

 cut by the later cirques and canyons, but down the main divides one may 

 follow the older topography with moderate gi-ade to the gentle foot slopes, 

 remnants of which now form the beautiful benches that slope away from the 

 mountains at an angle of about 5 degrees, 100 feet or more above the present 

 stream valleys. 



In the southern section the altitudes are greater and the general topography 

 more rugged, but many of the ridges rise to fairly accordant levels, and here 

 and there small remnants of a flat surface occur at an altitude of about 10,000 

 feet. The main divides descend to gently sloping benches as in the north- 

 ern section. The truncation of widely different rocks and structures by the 

 older topography of mountain and bench land shows that the region was for- 

 merly subjected to extended erosion, sufficient to produce an early stage of 

 penejilanation. The superior hardness of the central cores of the moiuitaiiis 

 permitted the latter to retain subdued mountainous relief, for the summits 

 now lie 3,000 to 4,000 feet above the upper limits of the benches. 



REVIVAL 



After peneplanation the region was revived. Two well defined sets of rock 

 benches, lower than the ones already described, show that thei'e were at least 

 two periods of erosion before the present one. The earlier of these appears 



