PRR-MOENKOPI UNCONFORMITY OF COLORADO PLATEAU 71 

 AREAL EXTENT OF THE UNCONFORMITY 



Many other workers who have studied the stratigraphy of this 

 region have recognized the prevailing unconformity at the base 

 of the Moenkopi, but in general it has heretofore been considered 

 a minor break. The evidence goes to show that it is recognized 

 over an area from the Little Colorado River in Arizona, east to the 

 Zuni Uplift in New Mexico, and northwest to the Dirty Devil 

 (Fremont) River in Utah. 



Fig. 7. — Cross-bedded sandy shale (the two dark masses to the left of the 

 center) resting in erosion channel in Kaibab limestone; dune sand in the foreground. 

 On Little Colorado River, near Tolchico, Arizona. 



In the San Juan Oil Field, which lies about midway between the 

 Ramah and Fruita localities, the Moenkopi, according to Woodruff,^ 

 rests on the Goodridge (Redwall ?) limestone with "a sharp litho- 

 logic break," though he does not mention an actual erosion interval. 

 Of the same place Gregory^ says : " No undisputed evidence of uncon- 

 formable relations between the Pennsylvanian and Permian ( ?) 

 was obtained at this locality." He indicates, however, evidence 

 of a probable break of importance in sedimentation. In view of 



' E. G. Woodruff, "Geology of the San Juan Oil Field, Utah," C/.5, Geo!. Surv., 

 Bull. 471, p. 87. 



* H. E. Gregory, op. cit., p. 21. 



