472 EEPOET UNITED STATES GEOLOGICAL SURVEY. 



and nortliwest. Throughout, its character is broad, flat, and ill-defined. 

 It enters the Park on the west, on an elevated plateau west of the 

 Lower Geyser Basin, a plateau of volcanic rock, densely covered witli 

 timber, and cut by numerous abrupt canons, but nearly destitute of 

 water. Along this plateau the divide trends very nearly south. Eeach- 

 ing the heads of the Firehole and of Bechler's Fork, it turns to the east 

 and then to the north, to pass around the head of Shoshone Creek. 

 Here it changes its character, and becomes a rather sharp ridge, the 

 sides of which are deeply cut by small gulches, producing an endless 

 amount of small detail in the topography. North of the eastern part of 

 Shoshone Lake the divide again makes a decided change in direction, 

 returning almost upon itself, and thence runs in a general southeast 

 direction across the remainder of the Park, leaving it at a point south of 

 the south arm of Yellowstone Lake. From the turning point down to 

 Flat Mountain, the divide is somewhere on a broad, rolling swell, the 

 highest point of which is but slightly above Yellowstone Lake. Over 

 a breadth of several miles there is scarcely any perceptible slope, and 

 the broad swell is dotted with lakelets and marshes having no outlets. 

 From the north, the elevation of this portion of the divide decreases 

 southward, reaching its lowest point near Lake Riddle, a lakelet with- 

 out outlet, at an elevation of 8,000 feet above the sea. This name like 

 the " Great American Desert," has been driven from point to point, find- 

 ing, like the Wandering Jew, no abiding place, until finally Professor 

 Bradley rescued it from its peripatetic career, attaching it to this insig- 

 nificant lakelet, where it is not likely ever to be disturbed. Among 

 its past glories, it is to be recorded that on many maps what we now 

 know as Yellowstone Lake appears as Lake Eiddle. Flat Mountain, 

 which next bears the main watershed, is, as the name implies, flat. Its 

 broad-timbered summit covers several square miles, while its slopes, 

 which on all sides but the north are very gentle, make the mountain 

 cover a large area of country. The northern slopes, at the base of which 

 lies the Flat Mountain arm of Yellowstone Lake, are rugged and pre- 

 cipitous. By some of the earlier expeditions, e. </., Doane's, 1870, and 

 Barlow & Heep's, 1871, this mountain was called Yellow Mountain 

 from the color of the volcanic rocks on the north face. This name, how- 

 ever, seems to have fallen into disuse. 



Southeast of Flat Mountain, the divide follows the crest of a range 

 of rounded hills, timbered to the summits, which carry the watershed 

 outside of the Park. 



THE YELLOWSTONE DRAINAGE AEEA. 



The Yellowstone Eiver heads in Bridger Lake, southeast of the Park, 

 and in the mountains in its neighborhood. One of the forks of the 

 well-known "Two Ocean Creek" also contributes to it. This part of 

 the stream, above Yellowstone Lake, is commonly known as the Upper 

 Yellowstone Kiver. Its course is slightly west of north, in a valley 

 averaging about 2 miles in width, sharply defined by mountain walls 

 which rise abruptly on each side to great heights. The eastern wall is 

 the rugged, volcanic Yellowstone Eange, whose peaks reach altitudes 

 exceeding 11,000 feet ; while on the west there is an abrupt descent to 

 the valley of a high undulating country, approaching a plateau in char- 

 acter, and of a height of 9,000 to 10,000 feet. The stream is sluggish, 

 and much of the valley, especially in the lower part, is very marshy, so 

 as to be practically impassable. Throughout, it is densely timbered. 



The drainage area of this system comprises more than half the area 

 of the Park, being 1,900 square miles. 



