GEOLOGY OF THE HAYSTACK STOCK 195 



this plateau is from 9,000 to 10,000 feet above sea level and numerous 

 peaks are higher. Of these the most conspicuous are Haystack 

 Peak, Little Haystack Peak, and Baboon Mountain. Many canyons 

 traverse the plateau and are sunk from 2,000 to 3,000 feet below the 

 level of the upland. They are narrow, U-shaped, and their walls 

 are very steep, even to the sources of the streams. The trees are 

 mainly spruce, white bark pine, and lodge-pole pine. They are 

 comparatively small and are valuable only for local use in connection 

 with the nearly dormant mining industry. Aspens and willows grow 

 in the marshes along the streams, and above 9,500 feet the vegetation 

 consists chiefly of small junipers and stunted cedars. 



Drainage. — The Boulder River is the most important stream of 

 the area; rising south of Haystack Mountain it flows northward 

 through the Snowy Range and enters the Livingston River at Big- 

 timber. Several tributaries join the Boulder River from the west, 

 among which are Elk Creek, Copper Creek, and Sheep Creek. 

 From the east its afliuents are East Fork and Basin Creek. The 

 southeastern portion of the area mapped is drained by Slough Creek 

 which, flowing southward, joins the Yellowstone River in the Yellow- 

 stone National Park. Haystack Basin lies between Haystack Peak and 

 Baboon Mountain. A low ridge, trending north and south, forms a 

 watershed west of which the drainage is through Basin Creek into 

 the Boulder River. 



Effect of character of rocks upon topography. — The stock of Hay- 

 stack Basin, especially the coarse-grained central portion, weathers 

 very readily, falling into coarse arkose and consequently forms a 

 relatively low area. The eruptive rock around the stock is very 

 resistant, since it has been indurated at the contact and it forms 

 the mountain crests to the north and to the south of the basin. Else- 

 where, the breccia and minor intrusives appear to have been eroded 

 at about equal rates. Dikes seldom stand out conspicuously above 

 the surface, and other intrusives, aside from the Haystack stock, do 

 not find marked expression in the topography. Sedimentary rocks 

 have only a small areal distribution. They are nearly flat and do 

 not form notable physiographic features. They outcrop only on 

 the sides of the canyons and are represented by a quartzite member 

 which usually forms a bench, above which is a ledge of lim.estone. 



