HISTORY OF DEFORMATION IN GREAT BASIN PROVINCE 245 



In the Colorado Plateau region Dutton* finds that from the Carbon- 

 iferous to the Cretaceous there was physical rest, but at the close of the 

 Cretaceous, simultaneously with the Wasatch uplift, there occurred, on 

 a comparatively slight scale, uplifting, flexing, and dislocating, followed 

 by erosion. 



EOCENE MOVEMENTS 



The Eocene was a time of considerable disturbance in the Great basin. 

 In the early part of the period the Vermilion Creek sediments were laid 

 down in the Ute lake, with their westernmost and thickest portion near 

 the Wasatch. The deposition of these beds was stopped by a period of 

 folding along the western shore, during which the country west of the 

 Wasatch sunk so that the Eocene waters ran 200 miles westward into 

 Nevada, forming part of the Gosiute lake, in which was deposited the 

 Green River Middle Eocene.f 



After the Middle Eocene sediments had accumulated they w^ere up- 

 heaved and bent into folds having as much as 40 or 50 degrees dip. 

 This disturbance may have extended farther west, into the region of no 

 known Eocene deposition, but there is no means of judging. 



The belt of Triassic and Jurassic marine sedimentation in western 

 Nevada and adjacent California, defined, according to King, by the ele- 

 vation of eastern Nevada at the close of the Carboniferous, became shut 

 off on the west and transformed into an elevated trough by the uplift of 

 the Sierra Nevada at the end of the Jurassic. This depression was ap- 

 parently above the sea during the Cretaceous and early Eocene, for no 

 deposits of these periods have been discovered in it. But during late 

 Eocene there were laid down in it extensive lake beds, which are found 

 at intervals from the Silver Peak range southeastward into the Mqjave 

 desert, and these were followed by later Tertiary strata, so far little studied. 

 Thus the present rather scanty evidence points to the close of the Middle 

 Eocene as the time when the post-Jurassic depression was remodeled 

 into a lake basin. The differential subsidence which effected this was 

 therefore contemporaneous with the movement which according to King 

 closed the existence of Gosiute lake. The general trough apparently ex- 

 tended at this period southeastward into the Mqjave desert and Mexico, 

 where the lake beds are replaced by Upper Eocene marine sediments, 

 overlain by marine Miocene. The depression thus formed has persisted 

 through Tertiary and Pleistocene time to the present day. It is now rep- 

 resented in Mexico by the gulf of California, and in California and Nevada 

 by the Colorado and Mojave deserts and that relatively sunken western- 

 most belt of the Great basin which borders the Sierra Nevada. 



* Second Ann. Rept. U. S. Geol. Survey, p. 65. 

 t King : Op. eit., pp, 747 iind 755. 



