36 BUREAU OF AMERICAN ETHNOLOGY [bull. 54 



representing differential erosion of alternating hard and soft zones, 

 rising one above another to the rim of the canyon. Along the base 

 of the cliff, cones or "tent rocks" of tufa have been partially isolated 

 from the canyon wall. Their origin is somewhat similar to that of 

 ''monument rocks" in certain parts of the West. Fragments of the 

 harder upper tufa, sliding down steep slopes, came to rest, affording 

 protecting caps for the soft tufa beneath them. Storms beating 

 upon the portions of the slopes not thus protected wore away the 

 material around the protected spots, leaving the latter standing out 

 above and partially isolated from the slopes. The effects of this 

 process, which is still m active operation, may be observed in all 

 stages. Some of these cones are also developed by the dissection 

 of the cliff immediately beneath a hard cap, a fragment of the cap 

 rock being left in place by the weathering process. The south wall 

 of the portion of the canyon where the ruins occur is notable for 

 the absence of terraces, cliff, and cones, as just described, in place of 

 which there is a fairly uniform slope of 35° to 45° from the hori- 

 zontal. It is sparsely covered with pinon pines, cedars, shrubs, and 

 other vegetation. 



The recurrence of the steep cliff in all the canyons of the region, 

 always on the north side, is an important feature of the environment 

 of the ancient inhabitants. The origin of this peculiar topographic 

 type is an interesting problem. Bandelier ^ attributed this condition 

 to the beating of heavy rains from the south and east. He surely 

 meant south and west, as storms from the south and east would pass 

 directly up the Frijoles canyon, which he was discussing, and be as 

 productive of results on one side as on the other. The prevailing 

 direction of storms is not sufficient to explain the cliffs, but may be 

 one factor. It is probable that several factors contribute to the 

 final result. 



A study of the recent meteorologic maps of the ITnited States 

 Weather Bureau ^ indicates that the prevailing winds are southwest. 

 During the writer's visit to the region in August, 1910, the rain- 

 storms came from' west and southwest. Such storms, striking the 

 north wall of the canyon at a high angle, would affect it more rad- 

 ically than the south wall, washing away much of the debris from 

 the slopes and thus contmually exposing fresh surfaces to subaerial 

 erosion and at the same time preventing the accumulation of the soil 

 necessary for the growth of a protecting blanket of vegetation. 

 These storms would also actively erode the soft lower tufa more rap- 

 idly than the upper hard part, thus tendmg to form a cliff. The 

 wind also would work in the same way. The opposite side of the 



1 Bandelier, A. F., The Delight Makers, p. 1, 1890. 



» Linney, Charles E., Climate and Crop Service of the Weather Bureau, Annual Summary, New Mexico 

 Section, 1905, 1906, 1907, 1908, and 1909, U. S. Dept. Agr. 



