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YEARBOOK, PUBLIC MUSEUM, MILWAUKEE 



[Vol. II. 



there is a deep depression in the plateau level caused by the weakening 

 of the rock along this break. This is called the Muav Saddle, and con- 

 nects an outstanding part of the plateau known as the Powell Plateau 

 with the main mass of upland to the northward. This Powell Plateau 

 is a long and rather narrow projection ,of the northern rim, which 

 slopes perceptibly to the southwest. It is almost completely encircled 

 by the river and canyon which here make a very large detour. 



The point where this fault crosses the canyon wall is the division 

 line between the Kaibab Division of the Grand Canvon and the Kanab 



.atSS 



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J 



Fjg. 61. — The Powell Plateau from Pima Point, Grand Canyon. The 

 downward bending of the strata of Powell Plateau as they approach the 

 West Kaibab Fault can be seen at the right of this figure. 



Division lying to the westward. This division line is not an imaginary 

 one, but is reflected immediately in the structure of the walls of the 

 canyon. Throughout the entire Kaibab Division and as far westward 

 as this point, the Tonto Platform, cut in the green shale of the Tonto 

 group, has been the prominent horizontal ,of the canyon wall, but here 

 the rocks of the Tonto Division become more and more sandy and 

 capable of resisting erosion so that they begin to form a more perpen- 

 dicular cliff. At the same time rocks higher up in the canyon wall in 



