HAOTOB. 



MAMMOTH HOT SPRINGS. 349 



Bnnsen peak. Terrace mountain is an outlying mass of the plateau, 

 formed ofrhyolite and capped at its northern end by travertine. The 

 diff oil the southern en 1 of the summit of Mount Evarts is a thin 

 extension of the great rhyolite lava sheet, separated from the main mass 

 by tin 1 erosion of Lava creek. 

 'Within a lew miles of the Mammoth Hot springs are several beauti- 

 ful waterfalls, formed by the waters of the plateau leaping over walls 

 of compact basalt in their descent to the lower country. Among them 

 may be mentioned Osprey falls on the Gardiner river, and Undine 

 falls on Lava creek, both of which are well worth a visit. 



MAMMOTH HOT SPRINGS TO NOR1US BASIN. 



Leaving the Mammoth Hot springs (0,250 feet ), the road gradually 

 ascends over rliyolitic rocks more or less covered by alluvium and 

 glacial debris. On the west side of the road, just before reaching the 

 Golden Gate, immense blocks of travertine may be seen piled up one 

 upon the other in a confused mass in a manner at first difficult' to 

 understand. They are best explained by supposing them to have been 

 thrown forward from Terrace mountain by some sudden earthquake 

 shock which thrust the easily displaced rock from its original position 

 down the side of the mountain. 



At Golden Gate the road enters the picturesque gorge of Glen creek, 

 which separates the plateau escarpment from Terrace mountain. At the 

 upper end of this gorge the road enters upon the open grassy plain of 

 Swan bake valley (7,200 feet), a northern extension of the plateau. A 

 narrow ridge of andesitic rocks— a spur of Sepulchre mountain— shuts 

 in the valley on the west. Opposite Swan lake andesite gives way to 

 rhyolite, which in turn is replaced by basalt, forming the extreme 

 southern end of the ridge and falling away gradually to the level of the 

 plain. This basalt, in thin flows, stretches across the valley, and its 

 southern limit is sharply defined by the course of Gardiner river. The 

 valley is strewn with glacial drift from the Gallatin mountains, and 

 evidence of ice movement is everywhere to be seen, especially in low 

 morainal ridges trending across the valley, which are shown in cross 

 section by the wagon road. From Swan Pake valley a tine view is 

 Obtained of the Gallatin range to the west, extending all the way from 

 Electric Peak (11.125 feet) to Mount Holmes (10,578 feet) a distance of 

 13 miles in an air line. Snow lies upon the higher summits well into 

 midsummer. 



Crossing Gardiner river, the road passes up the valley of Obsidian 

 creek, the lower part of which is known as Willow park, a long strip 

 of meadow land the borders of which are in great part covered with 

 a luxuriant growth of willow, beyond which rise the stately pines of 

 the plateau. The scenery now assumes a monotonous appearance, due 



