GEOLOGICAL SURVEY OF THE TERRITORIES. 131 



miles, sketcliing every bay or indentation, as well as tlie mountains that 

 inclose it. The topographical survey was continued around the south 

 and west shores of the lake with perfect success. A series of careful 

 observations for elevations were taken at all our permanent camps, as 

 well as at other suitable localities j so that the height of the lake above 

 the sea may be regarded as very accurately attained. 



A small party in charge of Mr. Stevenson returned from Hot Spring 

 camp to Bottler's Eanch, by way of the west side of the lake, to obtain 

 additional supplies. On tlie evening of August 9, we camped at the head 

 of the main bay, west of Flat Mountain. Our hunters returned, after 

 diligent search for two and a half days, with only a black-tailed deer, 

 which, though poor, was a most important addition to our larder. It 

 seems that during the months of August and September the elk and 

 deer resort to the summits of the mountains, to escape from the swarms 

 of flies in the lowlands about the lake. Tracks of game could be seen 

 everywhere, but none of the animals themselves were to be found. 

 Our course around the lake was intended to follow the shore as far as 

 possible. We made our way among the dense pines or over the fallen 

 timber, sometimes in grassy glades, through marshes, or by lily-cov- 

 ered lakes. The little streams, which are at this season mostly dry, 

 have worn deep gullies through the superficial beds, showing the old 

 lake deposits to have been from 200 to 600 feet in thickness. 



At sunrise on the morning of August 10, at the west base of Flat Moun- 

 tain, the thermometer stood at 15 Jo, and water was frozen in my tent one- 

 fourth of an inch thick. The rocks of Eed Mountain are trachyte, with 

 a purplish tinge, quite hard, and somewhat spotted and banded. Some 

 portions of the mountain are very red, and from this fact it derives its 

 name. Those of Flat Mountain are the same in texture and color. From 

 the summit of Flat Mountain we had an excellent view of the lake. Three 

 islands were visible, one of them quite small, 200 yards long, covered 

 with pine timber. It is really an elevated ridge of sand. The other 

 two are about a mile in length, also covered with a dense growth of pines. 

 Along the shores of these islands are bluff banks of stratified volcanic 

 sand, 50 feet high. All these islands are probably elevated i)ortions of 

 the old lake-bed, which have gradually risen above the surface as the 

 waters of the present lake diminish. To the vv^estward a still higher 

 range can be seen, and near it Heart Lake, and still further west Mad- 

 ison Lake, embosomed among thie mountains. On the long iDoints or 

 fingers, as it were, that extend out into the lake, are several small lily- 

 ponds, and open meadow-spaces, covered with thick grass. The general 

 view, however, consists of an outer range or rim of volcanic peaks, from 

 10,000 to 11,000 feet high, with the inner portions, or belt of lower hills 

 and ridges, black with the dense forests of pine, but relieved here and 

 there by a small lake, or an open meadow glade. The altitude of Flat 

 Mountain is 9,704 feet. 



From this high point, with the grand basin spread out before us, we 

 may again ask a question in regard to its origin. On all sides, and 

 among the foot-hills, the debris, which consist of fragments of trachyte^ 

 are enormous. Steps produced by slides can be seen most clearly by 

 looking over the dark mass of pines. We still believe that tlie basin 

 was at first a depression, produced by the action of the volcanic forces 

 which built uj) the surrounding groups of mountain peaks, aud formed 

 a reservoir for their drainage, but that it is also due in part to erosion. 

 A vast amount of material has been ground up by the waters of the lake 

 from the sides of the basin, to form the extensive modern deposit which 

 we meet with everywhere. 



