132 DESOIJIPTIVE GEOLOGY. 



open basins, shut in by high liills, which are usually filled with recent Qua- 

 ternary deposits, and form a characteristic feature of the region. Encamp- 

 ment Meadow is a little mountain-valley, having some few acres of grassy 

 bottom at the head of Grand Encampment Creek. Grange Valley, east 

 of Davis Peak, is another basin of similar character. 



The high ridges and mountain-slopes are generally covered with a 

 good growth of coniferous forests up to about 11,000 feet, the average 

 height in these latitudes in the Rocky Mountains, although varying some- 

 what with the exposure. The higher plateaus and summits are mostly bare. 

 On the western slopes, the growth would appear to be quite dense, but per- 

 haps not so vigorous as on the opposite side. The same species are found 

 as characterize the Medicine Bow and Colorado Ranges. 



Geological Description. — In its geological structure, the Park Range 

 for its entire distance belongs, like the other great uplifts to the eastward, 

 to the Rocky Mountain system of highly crystalline rocks of Archaean age. 

 Rocks of later ages form but a very subordinate part of the uplift, and are 

 found only along the lower flanks, seldom rising more than a few hundred 

 feet above the plain, where they rest unconformably at varying angles upon 

 the older series. 



At the extreme southwest corner of the Park, Tertiary basaltic rocks 

 conceal the spurs of the Archaean series; but in one instance only, at 

 Rabbit Ears Peak, do they form any considerable part of the slope. 



Farther to the north, between Cheyenne and Arapahoe Creeks, the 

 Dakota sandstones occur inclined at a high angle. Still farther north- 

 ward, rocks as low as the Red Beds of the Triassic, with the conformable 

 series exposed, as high as the Colorado marls, are found uplifted against the 

 granites, while near where the Platte River leaves the Park, the Colorado 

 beds appear lying next the Archaean. Above these, the horizontal beds of 

 the North Park Tertiary, which cover the Mesozoic rocks of the Park 

 Basin, lie up against the Archaean, concealing the older rocks, and breaking 

 the continuity of their exposures. 



Over that portion of the Park Range north of the Park, the later 

 sedimentary beds have never extended, except possibly in some lower 

 portions, which cannot now be traced. To the north and east, the h6ri- 



