1922] Vaughan: Geology of San Bernardino Mountains 393 



A large mass of "caliche" or limestone fanglomerate lies between 

 Cushenbury Springs and Grapevine Creek and extends northward 

 three miles from the mouth of Blackhawk Canon. It has been exten- 

 sively dissected, but remnants still extend high on the steep slope. 

 In some portions of this mass there is considerable limonite, so that it 

 appears to form the cementing material for the limestone fragments. 



Pig. 9. Section three-quarters of a mile southeast of Smart's Ranch. 



Alluvium 



Alluvial fans are being deposited in the San Gorgonio Pass on the 

 south side of the range and also along the north flanks and in the 

 Mohave Desert. Since they not only represent sedimentary deposits 

 but are important as physiographic features, they have been discussed 

 in that connection and need no further description. 



Smaller areas of alluvium are found in Bear and Holcomb valleys, 

 Santa Ana Canon, Morongo Valley, Cienaga Seca, Broom Flat, and 

 other swampy places in the mountains. 



Structure 



Folds modified by intrusions and faults. — The older sediments of 

 the region, the Arrastre quartzite, Furnace limestone, and Saragossa 

 quartzite, have been folded and faulted and the resulting structure 

 further complicated by granitic intrusions. The axis of a northwest- 

 southeast syncline passes a little to the west of Doble (fig. 5 and section 

 B-B'). The northeast limb can be followed southeastward to Round 

 Valley. Throughout this distance the limestone dips toward the Sara- 

 gossa quartzite at angles of from 20° to 60°, but does not always pass 

 beneath it, as may be seen south of Smart's Ranch, since the simple 

 relations are disturbed by strike faulting (fig. 9). 



