224 SOUTHERN CALIFORNIA GEOLOGY 



mountains of which these folds are a part were made in 

 some early stage of the Pleistocene epoch. The facts 

 concerning the origin of the Dominguez Range in the 

 latter half of the Pleistocene time have been given on 

 a previous page. 



There were several periods of movement in Pleisto- 

 cene time, but I have not as yet been able to fully con- 

 sider their definition and classification. This will un- 

 doubtedly be undertaken by future students. 



FAULT MOVEMENTS OF RECENT TIMES 

 Notwithstanding the fact that the great movements 

 took place in Pleistocene time, small fault displace- 

 ments of comparatively recent geologic age may be 

 seen at several localities in Southern California and 

 our occasional earthquakes testify that movements 

 may still sometimes take place along them. These 

 are observable as subparallel, rectilinear grooves in 

 scarps across some of the hills of folded structure 

 and alluvial fans, and their courses are sometimes 

 occupied by modern and but slightly indented drain- 

 ages. Grooves of this type may be seen east of the 

 summit valley on the east slope of the Baldwin Hills, 

 when observed in the proper light, and on the south 

 side of Dominguez Hill. Their general direction is 

 northwesterly and parallel to the trend of the range. 

 Recent fault phenomena are also shown in the old 

 talus fans along the southwest front of the San Ber- 

 nardino Range, and along the southwest scarp line of 

 the Badlands Range. 



Noble says that some of the recent scarps developed 

 along the San Andreas Fault along the north side 

 of the San Gabriel Range may date from the Fort 



