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University of California Publications in Geology [Vol. 13 



GEOLOGY 



General Statement 



North and northwest of Cienaga Seca Creek the rocks are limestone 

 and quartzite, presumably of Paleozoic age, intruded by granites. 

 South and east the rocks are mostly schists and granites, some of 

 which have been rendered gneissic, so intimately associated that they 

 have not been differentiated. They were originally thought to be pre- 

 Cambrian, but portions of the sediments to the north are so altered as 

 to be indistinguishable from them. This raises a doubt as to the age 

 of a large part of this southern complex, and, although parts of it 

 may be altered phases of the rocks to the north, it will be discussed 

 separately. The granitic rocks of the region represent several different 

 intrusions, but no evidence of sedimentation between them has been 

 found. 



Along the south flank of the San Bernardino Mountains there are 

 sandstones, shales, and fanglomerates of Tertiary and Quaternary age. 

 Remnants of basalt flows are also found here. In the desert to the 

 north, and also in scattered areas in the mountains, there are sediments 

 and basalt supposed to be correlative in a general way with those along 

 the south flank. 



The rocks of this region have never before been described, and local 

 names have been given them. The sedimentary formations involved 

 are, in chronological order beginning with the oldest, the Arrastre 

 quartzite, named after Arrastre Creek; Furnace limestone, after Fur- 

 nace Canon ; Saragossa quartzite, after Saragossa Spring ; Potato sand- 

 stone, after Potato Canon ; Lion sandstone, after Lion Canon ; Hath- 

 away sandstone and shale, after Hathaway Creek ; Santa Ana sand- 

 stone, after Santa Ana River ; Pipes f anglomerate, after The Pipes, a 

 watering place ; Deep Canon f anglomerate, after Deep Canon ; old 

 desert deposits ; Coachella f anglomerate, after Coachella Valley ; Cabe- 

 zon f anglomerate, after Cabezon Station ; Heights fanglomerate, after 

 Banning Heights ; glacial till ; alluvium. The igneous rocks are : a 

 heterogeneous mass of granites ; the Cactus granite, after Cactus Flat, 

 of rather uniform characteristics over large areas ; basalt. 



