102 Gregory — Igneous Origin of the " Glacial Deposits " 



General Geologic Relations. 



The members of the stratigraphic column represented in the 

 area under discussion embrace the following : the Goodridge 

 formation (Pennsylvanian) ; the Moenkopi formation and the 

 De Chelly sandstone (Permian); the Sbinarnmp Conglomerate 

 (Upper Triassic) ; the Chinle formation (Upper Triassic) ; the 

 La Plata Group (Jurassic) ; and the McElmo formation 

 (Jurassic or Lower Cretaceous). The Cretaceous strata out- 

 cropping at Carrizo Mountain and the Tertiary sediments of 

 the Boundary Mountains to the east, which doubtless formerly 

 extended over southern Utah and northeastern Arizona, are 

 not present in the Chinle Valley. The deposits of erratic 

 bowlders are associated with all the formations represented. 

 In the Mule Ear area they are found upon and within the 

 Moenkopi, the De Chelly, and the Chinle formations ; in the 

 Moses Rock field they occur upon and within the Moenkopi 

 and rarely overlie Goodridge strata. At Garnet Pidge the 

 Navajo sandstone, the upper member of the La Plata Group, 

 is dotted here and there with igneous erratics ; portions of the 

 McElmo floor are thickly strewn with bowlders, and beds and 

 lenses of "glacial conglomerate" are incorporated within the 

 McElmo sediments. 



Structurally the area under discussion is part of the Monu- 

 ment uplift, the eastern border of which is outlined by the 

 Comb Monocline. In the Moses Rock field the Moenkopi 

 strata dip eastward at angles of 4 to 20 degrees ; at Mule Ear 

 the beds are upturned at angles exceeding 50° ; Garnet Ridge, 

 on the back slope of the monocline, is composed of sedimentary 

 beds whose eastward dip averages between 2° and 3°. A fault 

 with slight displacement traverses the Moses Rock field, as 

 noted by Woodruff, and minor displacements of strata at Mule 

 Ear and Garnet Ridge, accompanied by landslides, have resulted 

 in producing masses of jumbled rocks in greatly confused 

 arrangement. 



Description op the " Glaciated " Areas. 



The Mule Ear Field. 



As mapped by Woodruff, the " glacial " deposits at Mule 

 Ear Pass cover an area of about one-fourth of a square mile 

 and rest " in an old channel carved in the Moencopie and Dol- 

 ores formations."* Approaching this field from the south, 

 attention is attracted to the high ridge forming the west wall 

 of the pass, and trending parallel with the dominating cuesta 

 of Comb Monocline (fig. 2). Throughout its course, for many 

 miles, this ridge is formed by upturned edges of massive De 



* Bull. 471, p. 86. 



