1922] Vaughan: Geology of San Bernardino Mountains 379 



of the range it is uniformly finer, contains fewer pebbles, and has a 

 better defined bedding. The general attitude of the formation is flat- 

 lying with minor warping, the dip locally being as high as 45°. 



About a mile below the houses in Big Meadows and on the south 

 side of the stream the sandstone again outcrops from beneath the 

 fanglomerate. Here it lies horizontally. Just below the junction of 

 Fish Creek and the Santa Ana River it strikes north and south and 

 dips 22° west. 



The formation cannot be correlated with much certainty with any 

 other in the district. That it is now in an abnormal position is strongly 

 emphasized by the fanglomerate, containing huge blocks of granite 

 over eight feet across, which overlies it unconformably and which, of 

 course, is the type of deposit one would expect to find between two 

 high ridges. The sandstone and shale may possibly have been formed 

 at the same time as the Hathaway formation on the south side of the 

 range, since their lithologic similarity indicates somewhat similar con- 

 ditions of deposition ; i.e., they were both deposited in a region of low 

 relief and, therefore, must certainly have been laid down before the 

 uplift of the mountain mass. Their degree of deformation also sug- 

 gests synchronous deposition. The present position of the evenly 

 bedded sandstone and shale in the bottom of a deep canon can only 

 be explained by faulting. The nature of this faulting will receive 

 further attention in discussing the structure of the mountain range. 



Pipes fanglomerate. — On the hill half a mile southeast of The 

 Pipes there is a flat-lying sedimentary deposit having a total thick- 

 ness of about 50 feet. The lower fifteen feet is a sandstone containing 

 many rounded pebbles. This grades up into a conglomerate consisting 

 for the most part of rounded granite, aplite, and quartz pebbles rang- 

 ing in size up to six inches in diameter. The upper part contains 

 considerable angular material. The lower sandy portion is grey in 

 color, but the upper is reddish due to the presence of hematite, prob- 

 ably derived from the overlying basalt. The larger part of the mass 

 is rather well cemented and more resistant to weathering than the 

 underlying granite, so that it forms a distinct bench near the top of 

 the ridge. 



At the table-topped hill directly east of The Pipes the basalt rests 

 on sandstone and fanglomerate having a thickness of 60 feet on the 

 south side but less than 20 on the north. The fanglomerate consists 

 for the most part of coarse granitic material, the larger fragments 

 attaining a diameter of about six inches. Below this there is about 

 15 feet of soft sandstone also consisting of granitic material. 



