134 GEOLOGICAL HISTORY OF THE YELLOWSTONE PARK. 



by nearly 2,0U0 snuaic. miles. The Fark plateau, with the adjacent 

 mountains, presents a sharply defined region, in strong contrast with 

 the rest of the northern Rocky Mountains. It stands out boldly by 

 itself, unique in topogTaphical structure, and complete as a geological 

 problem. 



The central portion of the Yellowstone l*ark is, essentially, a broad, 

 elevated, volcanic plateau, between 7,000 and 8,500 feet above sea-level, 

 and with an average elevation of about 8,000 feet. Surrounding it on 

 the south, east, north, and northwest, are mountain ranges with culmi- 

 nating peaks and ridges rising from 2,000 to 4,000 feet above the 

 general level of the inclosed table-land. 



For present purposes it is needless to confine ourselves strictly to 

 legal boundaries, but rather to consider the entire region in its broader 

 physical features. It is worthy of note, however, that by the proposed 

 enlargement the protected area will agree closely with the geographical 

 province. 



South of the I'ark, the Tetons stand out prominently above the sur- 

 rounding country, the highest, grandest peaks in the northern Rocky 

 Mountains. The eastern face of this mountain mass rises with nn- 

 riv^alled boldness for nearly 7,000 feet above Jackson Lake. I^i'orth- 

 ward, the ridges fall away abruptly beneath the lavas of the Park, only 

 the outlying spurs coming within the limits of the reservation. For the 

 most part the mountains are made up of coarse crystalline gneisses and 

 schists, probably of Archean age, flanked on the northern spurs by up 

 turned Palieozoic strata. 



To the east, across the broad valley of the Upper Snake, generally 

 known as Jackson Basin, lies the well-knowii Wind River Range, 

 famous from the earliest days of the Rocky Mountain trappers. The 

 Northern end of this range is largely composed of Mesozoic strata, 

 single ridges of Cretaceous sandstone penetrating still farther north- 

 ward into the regions of the Park, and protruding above the great 

 flows of lava. 



Along the entire eastern side of the Park stretches the Absaroka 

 Range — so-called from the Indian name of the Crow Nation. The 

 Absaroka Range is intimately connected with the Wind River, the two 

 being so closely related that any line of separation must be drawn 

 more or less arbitrarily, based more upon geological structures and 

 fo^ms of erosion than upon i^hysical limitations. 



The Absarokas offer, for more than 80 miles, a bold, unbroken bar- 

 rier to all western progress; a rough, rugged country, dominated by 

 high peaks and crags from 10,000 to 11,000 feet in height. Only a 

 few adventurous hunters and mountaineers cross the range by one or 

 two dangerous, precipitous trails known to but few. The early trap- 

 pers found it a forbidding land; prospectors who followed them, a 

 bnrren one. 



At the northeast corner of the Park a confused mass of mountains 



