The Shinumo Area. 375 



cline dipping sharply northeastward. A few minor flexures 

 cross the area in a northwesterly direction ; all dip to the 

 southwest and are hardly more than gentle swells upon the 

 general warping. 



The Shinumo Area is a critical area for the study of the 

 topography within the canyon itself. It is here that the topog- 

 raphy undergoes a transition from the profile which is char- 

 acteristic of the Kaibab division to that which is characteristic 

 of the Kanab. 



In the eastern, or Kaibab, division of the canyon, the de- 

 scent of the wall is unusually abrupt throughout the entire 

 Paleozoic rock series. The only bench or terrace of any 

 extent or definition is that which is developed near the bottom 

 of the canyon upon the summit of the basal sandstone of the 

 Tonto group. The bench is known as the Tonto platform ; in 

 it is cut an inner gorge, in which the river flows upon the base- 

 ment schists of the Archean. The platform averages a mile 

 in width on either side of the canyon, and is so well defined 

 that one may travel upon it throughout the length of the 

 Kaibab division. In the next western, or Kanab, division of 

 the canyon the lower terrace has disappeared. Instead, a 

 wide bench is opened out upon the summit of the hard red 

 sandstones of the Supai formation of the Aubrey group, about 

 a thousand feet below the level of the canyon rim. This 

 bench forms a broad level platform averaging two miles in 

 width on either side of the canyon, and has been named by 

 Dutton the "Esplanade." Through, it is cut a deep and narrow 

 inner gorge, at the bottom of which flows the river. 



The topography of the Kaibab division is characterized by 

 a much greater dissection than that of the Kanab ; great 

 amphitheaters are eroded back into the north wall, thronged 

 with buttes and outliers fashioned out of every formation of the 

 Paleozoic rock series and trenched by a multitude of side 

 gorges. The topography of the Kanab division is very simple, 

 consisting only of a broad outer canyon in which is cut the 

 inner gorge; the great dissection which makes the fantastic 

 scenery of the Kaibab division is entirely lacking. 



Eastward from Havasupai Point in the Shinumo area the 

 topography in the canyon is that which is characteristic of the 

 Kaibab division. Westward, however, the upper platform or 

 "Esplanade" begins to appear. The Shinumo amphitheater, 

 which occupies the greater part of the area to be described, 

 presents a combination of both types of topography ; the great 

 dissection and the presence of the Tonto platform are features 

 characteristic of the Kaibab division, but the Esplanade charac- 

 teristic of the Kanab division is developed to quite an equal 

 extent upon the upper surface of the Supai sandstone. In the 



