SOUTHERN ARIZONA ROCKIES 



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sula. It is regarded as a branch of the main orogenic belt of Nevada 

 which continued southward into Mexico west of the Mexican geocyn- 

 cline. 



The Mexican geosyncline transgressed northward in Early Cretaceous 

 time, and considerable thicknesses of Lower Cretaceous elastics were 

 spread over southeastern Arizona. The geanticline on the west was a site 

 of much volcanism, and the volcanic materials contributed to the sedi- 

 ments of the geosyncline. The Concentrator volcanics of south-central 

 Arizona suggest that the volcanic belt continued northwestward into 

 Arizona. 



Generally mild deformation followed the Early Cretaecous volcanism 



and sedimentation, and then over most of the southeastern Arizona Upper 

 Cretaceous strata and volcanics were spread. In Early (?) Tertiary time 

 as part of the Laramide orogeny uplifts with attendant folding and thrust- 

 ing in the Mountain Region and Sonoran Desert occurred. This was 

 followed immediately by the intrusion of granitic stocks. 



Mid-Tertiary time was marked by a varied volcanic activity from place 

 to place, and finally in late Tertiary time block faulting of regional 

 character occurred and caused the widespread deposition of the Gila con- 

 glomerate. Some faulting continued in places during the Quaternary, 

 but this was a time chiefly of the development of extensive pediments 

 around the desert ranges. 



