98 G. K. Gilbert—The Colorado Plateau Province. 
bed-rock is soft. Their number is increased up to a certain 
Let us now direct our attention tu the region of the oi 
The Plateau province lay beneath the ocean up to the ¢ 
of the Mesozoic age. In early Cenozoic time it was mo y 
covered by fresh-water lakes, and was not greatly elevate “it 
In more recent epochs it has been very greatly, but beng. 
lifted, and the lakes have been drained. e erosion whl 
corraded by the rivers 
he greater tributaries of the Colorado have their me . 
in elevated mountains which are well supplied with rain. Thel? 
courses through the P] 
aridity. 
On the uplands which order the cafions the supply of — : . 
is so small and the declivity is so great that weathering 1s 1 
is scant; and, for the lack of these, weathering is reduced pte - 
minimum. The degradation of the surface is limited by! ae 
thering, 
ateaus traverse regions characterized by a 
3: 
| 
