CENOZOIC HISTORY OF WIND RIVER MOUNTAINS 151 
in level by some 400 feet. The cycle which produced No. 3 passed 
well beyond maturity, for the slopes joining 3 and 4 are gradual; 
and broadly opened valleys of No. 3 finger back into the area of 
No. 4. At the time of its completion the masses rising above its 
level were, besides the main range, the rolling hills which formed 
as a whole a dissected terrace at its south end, and occasional 
knobs along the Beaver Divide to the east. 
Today the remnants of No. 3 have a distinct slope away from 
the range, amounting to about 1° around South Pass City. The 
plain stands at about 8,000 feet between the Granite Hills and the 
main range, about 8,000 to 8,200 feet by South Pass City (the 
higher value at the base of the mountains), 8,200 feet between 
Beaver Creek and Twin Creek near O’Meara’s ranch, and 7,400 
feet along the upper Beaver near Atlantic City. Along the Beaver 
Divide it drops to 6,770 feet ten miles east of Atlantic City, and to 
6,600 east of Hailey (twenty-two miles northeast of Atlantic City). 
The Beaver today is flowing about 400 or 500 feet below the level 
of this plain. 
The drainage on the Beaver Divide plain is unknown. Pre- 
sumably it was radially away from the range. There is no evidence 
that the present arrangement of streams held at that time. The 
slope of the plain may or may not have been what it is today. 
There seems no way of deciding. 
This plain carries gravels on its surface only where it cuts 
Tertiary rocks and where these rocks contain conglomeratic layers 
which furnish gravel to the plain. 
Plain No. 2. Table Mountain Plain..—Below the Beaver 
Divide plain, or No. 3, a later plain (Figs. 3 and 4) was very 
generally developed over the Mesozoic and later rocks of the Wind 
River region. During this stage the Beaver Divide came into 
existence and the Wind River and Sweetwater drainage areas 
became distinct. From this time on the geological history in these 
two main basins is somewhat different, and the topographical 
forms are unlike. 
The condition of Plain No. 2 in the Sweetwater area is not 
* Since No. 2 is provisionally correlated with the plain of Table Mountain, west 
of Lander, it is also called the Table Mountain Plain. 
