1921] Frick: Faunas of Bautista Creek and San Timoteo Canon 315 



fault that runs northwest and southeast through Cajon and San 

 Gorgonio passes, touches interestingly on the geological history of the 

 region. His statement is in the main as follows : 



. . . A . . . crustal movement whose beginnings may [at least] have been con- 

 temporaneous with . . . [the uplifting of the San Bernardinos] resulted ... in 

 the formation of an irregular arched wrinkle extending from San Jacinto Moun- 

 tains northwest along the line of the Badlands, which separate San Timoteo Caiion 

 from San Jacinto valley. . . . This fold can be traced on the surface as the Bunker 

 Hill Dyke to a point nearly two miles somewhat south of west of San Bernardino. 

 It probably extends even farther ... as an underground feature .... This clay 

 and gravel ridge has been one of the most effectual of subsurface dams. . . . 



Before the San Bernardino Mountains were uplifted subaerial erosion had 

 reduced an earlier topography to a condition in which the valleys were wide and 

 generally level and the mountains low, although [on account of the granite rocks] 

 often steep. Fragments of this old landscape are, it is believed, still preserved in 

 practically the condition in which they existed previous to the deformation in . . . 

 some of the higher parts of the San Bernardino Mountains. . . . The topography of 

 these higher areas where it has not been altered by modern gorge producing agencies 

 ... is much like the region north of Elsinore [the Ferris peneplain] . . . and it is 

 believed that these two regions once formed a continuous surface. ... It seems 

 fair to assume about three thousand feet as the maximum relief on the [this] 

 old surface . . . now only 2000 or 2500 feet below San Bernardino. . . . Perhaps 

 bed-rock hills exist there ... or the bed rock floor of the middle valley may be 

 relatively smooth like that of the Ferris Valley .... The rocks of the upper 

 San Bernardino region may be subdivided into two general classes . . . those 

 which outcrop everywhere in the higher regions . . . [schists, gneisses, diorites, 

 marbles, quartz-porphyries, sandstones, and conglomerates] and the clays and 

 alluvium . . . [sands, gravels, and clays] which fill the valleys, underlie most of 

 the fertile mesas and form the greater part of the Badlands between San Jacinto 

 and upper Santa Ana valleys. But at their base [that is, of the Badlands] is a 

 rather wide-spread series of fine clays and shales . . . [and] from the fineness of 

 these . . . and the fact that they are bent into sharp folds we know that extensive 

 earth movements have taken place since their deposition, . . . that the clays are 

 older than the formation of the San Bernardino vallej'' and . . . mountains. . . . 

 They were likely deposited in a lake like Bear Lake, but much longer, and larger 

 on the old land surface of rather moderate relief . . . [which] probably occupied 

 the lowest of the valleys at that time; and within it islands of the granitic or 

 gneissoid bedrock rose perhaps as the Box Springs and Lake View mountains 

 now rise above the Ferris and San Jacinto plains. . . . 



Sometime after the deposition of the Badlands clays a crustal movement 

 began, which folded the clay and seems to have elevated the San Bernardinos 

 . . . until they stood above the adjacent valleys but were perhaps 2500 feet 

 lower than at present. It is probable that at the same time San Bernardino 

 Valley subsided somewhat, so that its rock floor, sheeted over by lacustrine silts, 

 stood at a lower elevation than before the movement. . . . Mountain streams cut 

 deep canons and carried the products of their erosional activity out into the 

 lowlands as they do now. This detritus . . . was probably not quite so coarse 

 as the fan material of today. It was widely distributed over the lowlands south 

 of the mountains, boulder beds, sand beds, and clays alternating in an uncertain 

 succession until many hundreds of feet of alluvium were piled up. 



