162 SOUTHERN CALIFORNIA GEOLOGY 



Mill Creek fault. It branches off in a more easterly 

 direction from the main rift at some point east of San 

 Bernardino, as will presently be more fully described. 



The main rift southeast of Mill Creek closely fol- 

 lows the south side of the Mill Creek Range, where its 

 presence is indicated by a steeply-sloping escarpment 

 of tremendous proportions, which rises between alti- 

 tudes of four thousand and eight thousand feet, and is 

 marked by wonderful truncated facets, as may be seen 

 north of Forest Glenn and Beaumont. To the east 

 of Pine Bench several other major faults occur, ap- 

 parently as easterly branches of the main rift, and 

 are accompanied by great valleys through which flow 

 the headquarters of San Gorgonio Creek. One of these 

 may be termed the Raywood Fault and another, which 

 passes through the north end of the Morongo Indian 

 Reservation, I have named the Potrero Fault. South- 

 east of the reservation the continuation of the San 

 Andreas Rift towards Whitewater Creek is compli- 

 cated by its junction with the Banning and other 

 faults. This I have not worked out in detail. 



The successive eastward branches from the main 

 fault along the southwest borders of the San Bernar- 

 dino Plateau have detached long and narrow physio- 

 graphic blocks from it. These lie apart as outlying 

 ridges, much after the manner of partially severed 

 slices from the end of the main highland. 

 MILL CREEK FAULT 



The Mill Creek branch of the San Andreas Fault 

 arises along the southwest escarpment of the San Ber- 

 nardino Plateau east of San Bernardino and proceeds 

 in a slightly south of east direction along the south 

 side of the plateau summit towards the north- 



