THE OROGENIC EPOCHS IN NORTH AMERICA 649 



Nearly all authorities agree in assigning this event to the 

 middle Tertiary, and by many it is referred to the close of the 

 Miocene period. In the John Day basin of central Oregon, accord- 

 ing to Merriam and Sinclair,^ gentle folding closed the deposition of 

 the early Miocene sediments, and preceded the Columbia lava out- 

 flows. In the northern part of the Cascade Mountains of Wash- 

 ington a similar event is recorded by Smith and Calkins.^ The 

 most accurate estimate of the date of the deformation seems to be 

 that which has been made in the Coast Range of southern California 

 by Arnold^ and others, who show that it followed the deposition 

 of the lower-middle Miocene sediments (Monterey shale), and 

 preceded that of the upper Miocene (Santa Margarita). 



Santa Barbaran orogeny (early Pleistocene). — -Recent studies in 

 the oil-bearing districts of southern California have brought to 

 light the fact that, although the region was considerably affected by 

 the Antillean orogeny, it was as much or even more closely com- 

 pressed after the deposition of the marine Pliocene formations. 

 Thus in the region about Santa Barbara, the Pliocene has been 

 not only folded but overturned, and locally lies beneath overthrust 

 masses of earlier Tertiary strata. In the Coalinga oil district'* on 

 the southwest side of the great valley of California, the effects of 

 the Santa Barbaran disturbance are much more pronounced than 

 those of the middle Miocene folding. 



Although it has long been known that warping, gentle changes 

 of level, and normal faulting proceeded on a large scale early in the 

 Pleistocene period, particularly in western United States, there 

 are but few places outside of California where actual folding has 

 been assigned to this age. Possibly we should refer to the Santa 

 Barbaran folding the gentle flexures in the late Miocene lavas of 

 central Washington and the Cascade Mountains, as well as the 

 latest gentle folds in the Olympic Range of the same state. To the 



' J. C. Merriam and W. J. Sinclair, Bull. Dept. ofGeol. Univ. ofCal., V (1907), 174. 



2 G. O. Smith and F. C. Calkins, U.S. Geol. Survey, Snoqualmie, Wash., Folio, 

 No. 139. 



3 Ralph Arnold, "Environment of the Tertiary Faunas of the Pacific Coast of the 

 United States," Jour. Geol., XVII (1909), 509-33. 



^Ibid., "Geology of the Summerland Oil District, California,"' U.S. Geol. Survey, 

 Bull. 321. 



