PAPERS ON GEOLOGY AND GEOGRAPHY 217 



openings were used by the ancient inhabitants of the region as 

 homes, who built walls across the front, appropriating the up- 

 per massive rack as a roof. This is true of all the canyon ruins, 

 the best example being Cliff Palace. 



The other characteristic method of erosion in the plateau 

 country is by cliff recession through stripping. The general 

 degradation of the Plateau Province is accomplished predom- 

 inantly by the erosion forces acting upon the almost vertical 

 edges of the strata where weathering, and wash, and wind is 

 especially effective. This sapping has gone on to an unusual 

 degree on the northern escarpment of the mesa where condi- 

 tions are very favorable. The almost vertical escarpment of 

 about five hundred feet of Mancos shale, capped by a heavy 

 sandstone, gives almost ideal conditions for cliff-recession. 

 As rapidly as the softer shale is carried away below, huge frag- 

 ments of sandstone slump off, making immense talus heaps 

 which in the aggregate resemble, somewhat, landslide topog- 

 raphy. These heaps are comparatively short-lived because there 

 is so little vegetation to protect them. The present mesa is 

 only a skeleton of what it was originally. It has been cut up 

 into many narrow strips by deep canyons which roughly par- 

 allel each other. These canyons starting at the Mancos in the 

 south have gradually worked their way headward until they 

 have cut through the entire present length of the mesa. This 

 cutting has gone on to such an extent that the canyon areas are 

 about equal to that of the remaining plateau surface. From the 

 standpoint of travel the region is as rough as most mountain 

 areas of the west. The canyon walls are the dominating ele- 

 ments of the relief, a relief produced by downward departures 

 from the general level, instead of an upward departure as is 

 common in mountainous areas. This gives an uncommon type 

 of topography. None of the canyons at the present time have 

 running water except during very severe showers. They are all 

 aggrading in the main and show considerable fill. Wells sunk 

 to the bottom of this loose material usually have sufficient 

 water to supply the stock foraging in the upper canyons. These 

 wells show from thirty to seventy feet of loose wash material, 

 according to Mr. Prater, who had the wells sunk. If his report 

 may be relied upon, and we believe it may, the canyons for- 

 merly were much deeper than now and must have carried much 

 more water. This points either to a much more arid condition 



