54 



SHORTER COXTRIBUTIOXS TO GENERAL GEOLOGY, rJ21. 



Canyon district. It contains deeply dissected 



areas in which the rocks are well exposed. 



The climate is arid, but farming by irrigation 



is very successful. Along Virgoi River and 



its few peremiial tributaries settlements are 



fairly numerous, but away from the streams 



there are none. St. George, the largest town 



in the region and the seat of Washington 



Comity, has about 2,000 inhabitants. Other 



smaller settlements are shown on the map 



(fig. 10). 



STRUCTURE. 



The dommating structural features of the 

 region arc the north-south faults of the Great 

 Basin system. The famous Hurricane fault 

 crosses it (see fig. 10) and, it is believed, the 



Grand Wash fault also. Other unnamed 

 minor faults are present. One prumuient 

 (old, kno\\ai as the Vu'gin antichne, extends 

 northeastward from the district a few miles 

 south of St. George almost to the Hm-ricane 

 fault — a distance of approximately 15 miles. 

 On this anticline cross folds have formed tliree 

 domes Icnowm as the Harrisburg dome, Wash- 

 mgton dome, and Bloomington dome. Other 

 minor folds occur here and there but are 

 relatively unimportant elements m the general 

 structure of the region. 



STRATIGRAPHY. 



GENERAL SECTION. 



The rocks of the region are classified in this 

 paper as follows: 



Geologic /oniiatio7ts of southwestern Utah and nnrthveslent Arizona. 



System. 



Quatornary. 



Tertiary(?). 



Cretaceou8(?). 



Jurassic. 



Series. 



Formation. 



Member. 



riiararter of rocka. 



Thirkness 



(feet). 



AlhuTum, dune sand. etc. 



Basalt flows with associated boulder beds 

 and cinder cones. 



Massive yellow sandstone with some pink 

 staining, separated by soft sandstone, 

 much of it red. and red shale. The 

 series as a whole is pink. 



Buff sandstones with some intercalated 

 shale. 



Variegated shale, with a little thin lime- 

 stone in upper part and some platy 

 limestone in lower part. 



1, 500+ 



1,000± 



140 



Greenish-gray, cream-colored, and Iirown 

 fossiliferous marine limestone, under- 

 lain by brick-red sandstone, shale, and 

 gypsum. 



460 ± 



Massive cross-bedded sandstone, red in 

 lower part and white above, the boun- 

 dary between the colored parts varying 

 in position from a level near the middle 

 to the top. 



100 



