GEOLOGICAL SURVEY OF THE TERRITORIES. 227 



as the outer slopes of tbe mountain, were well covered with tall pines 

 and spruces; while the higher portions had only scattered and stunted 

 trees and the crests were entirely bare, though enough dead stems of 

 small pines or cedars were found even there to make a small signal-fire. 

 The small plants of the summit are mostly of Alpine forms. Trails of 

 mountain-sheep were abundant, but the only vertebrate seen was a large 

 gopher, (?) very distinct from any species of which I have been able to 

 find a description, or figure, or mounted skin ; unfortunately, he escaped 

 my bullet. The elevation of the peak, as indicated by two readings of 

 my aneroid barometer, is about 10.600 feet. 



^o lines of outflow were traced down to the plain ; but, from the size 

 and position of the crater, and the character of the lava of its lower 

 portion, it is evident that ihis was a prolific source of the basalt which 

 so many times filled the great plain stretching off to the south and west. 

 The isolated cluster of mountains, about half way between this peak and 

 the Sand-Hill Mountains, has apparently the same structure, and may 

 have been another source of outflow. The lowest gap in the crater- wall 

 of Sawtelle's Peak faces northward; and the principal outflow of lava 

 was probably from that iioint, escaping thence down the valley of 

 Henry's Fork, though other portions may very probably have escaped 

 through subterranean passages and cracks in other directions, as is 

 frequently the case in those volcanoes whose modern eruptions have 

 given opportunities for the observation of their phenomena. The por- 

 tions of the lava next to the mountain and out to the center of the 

 valley are all pretty solid basalt, while the farther side of the valley- 

 deposits, and those which form the slopes of the eastern mountain, con- 

 sist of the older porphyries and volcanic sandstones. 



The peaks of the westward continuation of the range of which Saw- 

 telle's Peak forms the eastern termination show such structure, as seen 

 from a distance, as to indicate that they also are of volcanic origin, and 

 may have been other sources of the basaltic outflow. It is not known 

 to any of the present inhabitants of the region that any of these vol- 

 canoes have been active in modern times ; but Irving, in his Astoria, 

 states that Mr. Eobert Stuart, a partner of Mr. Astor in the Pacific Fur 

 Company, when crossing the mountain-range west of Pierre's Hole, in 

 the fall of 1812, " observed to the northwest, between Henry's Fort and 

 the source of the Missouri, several very high peaks covered with snow, 

 from two of which smoke ascended in considerable volumes, apparently 

 from craters in a state of eruption." The location indicated would apply 

 well to peaks of the range now under consideration. It is hardly to be 

 supposed that so experienced a mountaineer should have been deceived 

 by timber-fires, or that such fires should occur near the summits of peaks 

 covered with snow. * 



The ranges on the north and south sides of Henry's Lake are nearly 

 parallel, while the cross-range west of it is nearly at right angles with 

 them, thus giving a quadrangular form to the plain, which here termi- 

 nates the broad valley of Henry's Fork. From three points it has easy 

 passages to the neighboring valleys and the region beyond. From our 

 camp on the east side of the valley, Tyghee Pass, named for an old 

 Shoshone chief who was wont to use it, gives a smooth road, with very 

 gentle grades, into the valley of the Upper Madison. From the north 

 end of the lake, a broad, grassy plain, with scarcely a perceptible rise to 

 the divide, about four miles distant, shows a clear road to Virginia City 

 and the Lower Madison. This is called Eaynolds's Pass, from having 

 been used by that officer in his expedition of 1859-'60, and described in 

 his report. Tyghee Pass is also mentioned and mapped in that report 



