GEOGRAPHICAL DIVISIONS OF THE REGION SURVEYED. 11 
The region embraced in Captain Pope's explorations is thus divisible into three portions, dif- 
fering very considerably in their physical configuration. We have, first, the mountain ranges, 
with their intervening plateaux, extending from the valley of the Rio Grande to the Pecos; 
secondly, the elevated plateau of the Llano Estacado, from the Pecos to the Sulphur springs of 
the Colorado; and, thirdly, the descent or slope from this plain over the undulating and fertile 
valleys of the Texan rivers to the Red river at Preston, 
