HURRICANE FAULT IN SOUTHWESTERN UTAH 49 



— all of which will be briefly described below. The sequence 

 is as follows : 



(A) Early deformation and volcanic eruptions. 



(B) The first Hurricane faulting. 



(C) The inter-fault or plateau cycle of erosion, ending with basalt erup- 



tions. 



(D) The latter faulting. 



(E) The post-fault or canyon cycle of erosion. 



DEFORMATION AND VOLCANIC ERUPTIONS. 



a) Earlier foldi?ig. — The earlier disturbance of the strata in 

 the plateau province after their long period of quiet accumu- 

 lation resulted in a number of gentle folds and flexures with 

 slightly curved axes trending roughly north and south. In the 

 eastern regions, according to Button, these were monoclinal 

 flexures with a dip to the east by which a series of great steps 

 was formed descending from the then relatively high Basin 

 Range province to the lower Plateau province. In the Toquer- 

 ville district the folds became intensified and took the form of 

 well-arched anticlines and synclines. Among these more marked 

 folds, we are chiefly concerned with the most western — a shallow 

 syncline in which lies what now remains of the andesite mass of 

 the Pine Valley mountains, and the most eastern — a sharp anti- 

 cline that lies along the boundary between the Plateau province 

 of relatively level strata interrupted only by the gentle mono- 

 clines, and the broken Basin Range province. South of Toquer- 

 ville the sharp anticline faded out into a gentle eastward-dipping 

 monocline, while to the north the intensity of folding increased, 

 so that the anticline was steepened and finally at Kanarra com- 

 pletely overturned. The formation of these sharp folds seems 

 to have been due to an east-and-west tangential pressure whose 

 effects are confined to the immediate vicinity of the Pine Valley 

 mountains. 



b^ Andesite eruptio/is. — The mass of the Pine Valley moun- 

 tains, 3,000 to 4,000 feet thick, and twenty to thirty miles long, 

 is composed of a heavy sheet of andesite, called by the earlier 

 geologists a "trachyte." Wlierevcr its base is seen, the lava 

 lies upon a surface of Tertiary strata which seems to have suf- 



