PALEOGEOGRAPHY OF THE MESOZOIC 



511 



of the Comanchian seas, which are of the Atlantic-Tethyian realm, a 

 condition indicating that the two provinces were more or less, though not 

 completely, separated from one another by a land barrier, the Mexican 

 peninsula. 



Along the Pacific coast from San Luis Obispo County, California, 

 northward far into Oregon there is evidence of crustal movement during 

 Shastan time. Anderson states that the Knoxville is everywhere in this 



OROCRAPHY 



OF LATE 



COMANCHIAN TIME 



Figure 6. — Map showing Regions of Elevation {horizontal Shading and solid Black), 

 the Formation of the Coloradoan Oeosyncline (right-hand oblique Lines), and the 

 Pacific Overlap. 



Generalized from Ransome, "Problems of American Geology." The black area Is that 

 of the present Columbia River Plateau ; the region of elevation to the north is known 

 as the Northern Interior Plateaus, while that on the south is the Nevadan-Sonoran 

 region. 



area penetrated and disturbed by dikes and masses of serpentine and 

 peridotites. Moreover, in the Coast Range of southern California, where 

 these intruded rocks occur, the Horsetown strata are also absent, while 

 the Chico of Cretaceous time unconformably overlies the older formations. 

 In western Utah, eastern Nevada, and throughout Idaho uplift was 

 making itself felt as early as Middle Triassic time, forming the arch of 

 the Columbia River Plateau, which persisted into late Jurassic time (the 



