430 



STRUCTURAL GEOLOGY OF NORTH AMERICA 



shows them to have once covered the entire area. At all places observed, 

 there is a marked unconformity at the base ( Ransome, 1933 ) . 



Recause the Upper Cretaceous beds, where identified, rest in angular 

 unconformity on all the older rocks, it is concluded that crustal movements 

 of some proportions occurred about at the close of the Early Cretaceous. 

 Reeside ( 1944 ) shows central and southern Arizona out of water during 

 all but the last of Late Cretaceous time ( Fox Hills and Lance time ) , when 

 a trough in the site of the earlier one formed and sank at least 7500 feet. 

 It seems possible that the sediments could come from the geanticlinal area 

 on the southwest, but the spread of data does not preclude the existence 

 of land areas to the northeast of the trough. Ross ( 1925 ) believes a shore 

 line was immediately west of the Christmas-Ray-Miami districts, and 

 this is shown on the Late Cretaceous paleotectonic map as a narrow vol- 

 canic peninsula extending southeastward from the main geanticlinal area. 

 A northwest trend to the structures of central and southern Arizona had 

 thus become established. 



n*tn, 



MARBLE QUARRY SYNCLINE 

 PIPe 



Fig. 27.4. Mountains of southeastern Arizona. 



1939 ) composed of rhyolite, andesite, tuff, and arkose is considered Lower 

 Cretaceous here; some of the andesites of the Christmas area ( Ross, 1925 ) 

 may be Lower Cretaceous, and the Concentrator volcanics of the Ajo 

 district (Gilluly, 1946) are of the same age evidently. These are chiefly 

 andesites and keratophyres. It was a belt of andesitic eruptions, chiefly, 

 both of the explosive and passive kinds of activity. 



Upper Cretaceous strata have not been recognized in as many places 

 in southeastern Arizona and southwestern New Mexico as the Lower 

 Cretaceous, nor are they as thick where known; but Reeside's map ( 1944) 



Fig. 27.5. Section through Chiricahua Mountains showing Apache Pass fault (1) and Fort Bowie 

 thrust (2), after Sabins, 1957. Compare with Fig. 27.8. 



Section in the Mule Mountains showing angular unconformity between Lower Cretaceous 

 Morita fm (Km) and Paleozoic formations; also post-Lower Cretaceous thrusting. After Gilluly, 

 1956. 



