CENTRAL ROCKIES 



343 



Cedar Hills Orogeny 



!Fig. 22.17. Stratigraphic and structural relations in central Utah, in the Wasatch Plateau and 

 adjacent areas. Section 15, Fig. 22.1. After Spieker (1946) except for the designation of the 

 JCedar Hills orogeny. It is an idealized stratigraphic and structural diagram that extends from the 



Volcanism may have started in late Eocene time but the main eruptions 

 appear to be Oligocene. The volcanic rocks are elaborated on in Chap- 

 iter 36. 



SOUTHWESTERN UTAH 



The western margin of Colorado Plateau in southwestern Utah con- 

 jsists of a series of great steps eroded in the sedimentary rocks descending 

 southward. These steps are cut transversely by a few long, northerly 



Gunnison Plataau on the west to the Green River in the Colorado Plateau. Kt, Tuscher fm.; 

 Kmb, Buck tongue. 



trending faults of Mid- and Late Tertiary age (Fig. 22.19). Before the 

 faulting the western margin of the Plateau had been moderately folded, 

 which is a transition zone into a western belt of strong folding and 

 thrust faulting. The latter two belts are shown in Fig. 22.20. Following 

 the folding and thrusting the Claron conglomerate of Eocene (?) age 

 was spread over the beveled edges of the older formations. Mackin 

 (1960) views the Claron deposition to have culminated in an extensive 

 plain over much of southwestern Utah, upon which the later voluminous 

 ignimbrites spread. These volcanics are discussed in Chapter 36. 





