THE PRE-MOENKOPI (PRE-PERMIAN ?) UNCON- 

 FORMITY OF THE COLORADO PLATEAU 



C. L. DAKE 



Missouri School of Mines 



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There is a growing appreciation of the importance of the uncon- 

 formity below the "Red Bed" series of the Colorado Plateau 

 Province, as witnessed by the recent paper of Lee* on the subject. 

 During a reconnaissance in southeastern Utah, northeastern 

 Arizona, and northwestern New Mexico, the writer had an oppor- 

 tunity to gather some additional data on the extent and possible 

 magnitude of the stratigraphic break, and these facts are herewith 

 presented. 



The first part of the paper deals with the local evidences of 

 the unconformity at several points, particularly at Mule Twist 

 Canyon, Utah; at Fruita, Utah; in Quartzite Canyon, near 

 Fort Defiance, Arizona; at Ramah, New Mexico, on the Zuni 

 Uplift; and near Tolchico, Arizona, on the Little Colorado River. 

 The location of all these points is indicated on the accompanying 

 sketch map (Fig. i). 



The second part of the paper begins with a summary of the 

 known areal extent of the unconformity, and this is followed by a 

 discussion of the magnitude of the stratigraphic break. 



Since the formation names are largely local and probably 

 unfamiliar to most readers, the following partial columnar section 

 is given. 



Jurassic, La Plata sandstone 



^ . . f Dolores (Chinle) formation 



Tnassic, ^ 01 • 1 ^ 



[ Shinarump conglomerate 



. / pN / DeChelly sandstone (local) 

 ^'^' \ Moenkopi red beds 



' W. T. Lee, "General Stratigraphic Break between Pennsylvanian and Permian 

 in Western America," Bull. Geol. Soc. Am., Vol. XXVIII (1917), PP- 169-70. 



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