CHICKEN EIDGE. 191 



over 400 feet in precipitous walls, facing north and east, but on the south 

 falls away with debris slopes, permitting ascent to the summit. The mass 

 has a slight inclination to the east, and the greater part of it is lithoidal, 

 very brittle, and jointed in thin fissile layers. At a distance on the slopes 

 it resembles a debris pile of cherty indurated argillites. This rock is dark 

 gray in color, with small phenocrysts of feldspar and grains of quartz. 

 Obsidian and gray and red pumices are well shown here, with the varying 

 modifications found elsewhere in the Park and described in detail in 

 Chapter X of this volume. Mount Hancock is perhaps remarkable for the 

 variations in color of its obsidian. Black, brown, and various shades of 

 red are noticeable, and some of them when highly polished are singularly 

 brilliant, It is this dark, turret-like mass of rhyolite that makes Mount 

 Hancock so conspicuous a landmark over the Park region. The great 

 elevation and complete isolation of this small body of rhyolite are by no 

 means easy to explain. 



North of Mount Hancock the slopes of Big Game Ridge fall away 

 rapidly for 4 miles in long timber ridges, mostly buried beneath glacial 

 drift and soil. No rock exposures were observed other than the Montana 

 sandstones and the low rhyolite hills which border the uplifted sedimentary 

 beds. 



CHICKEN RIDGE. 



Chicken Ridge presents a narrow north-south chain of mountains 

 about 12 miles in length. It is a prominent and persistent orographic 

 block, with several culminating points between 9,000 and 9,600 feet above 

 sea level. Over the greater part of this area the mountain slopes are well 

 timbered and well watered. The southern end of Chicken Ridge rises 

 abruptly ou the east side of Snake River at its junction with Crooked 

 Creek, nearly due east of Mount Hancock. Along- its east base the ridge 

 is sharply defined from Two Ocean Plateau by the valleys of Crooked 

 and Grouse creeks and the narrow north-south depression lying between 

 the two streams. 



The Snake River fault, which is described later in this chapter, follows 

 the course of these streams, and the marked contrast, both geologically 

 and topographically, between the opposite sides of the fault serves to 

 accentuate the eastern boundary of the ridge. Northward Chicken Ridge 

 projects into Yellowstone Lake, and its gentle slopes along the base, with 

 broken, accidented hills rising above them, form the picturesque shores of 



