90 SOUTHERN CALIFORNIA GEOLOGY 



reros and valleys, some of which are of considerable 

 extent. 



The feature, as a whole, represents a segment of a 

 once more extensive land-surface which has survived 

 from Eocene time^ and which has since been cut into 

 parts by diagonal faulting. Its east side shows sug- 

 gestions of north-south faults which in the future 

 may probably be proved to be related to those of 

 the Basin Region. Its summit is diagonally crossed 

 and striped by fault scarps and valleys, the linea- 

 ments of which suggest relationships to the later- 

 made northwest systems, in so far as can be deduced 

 from the little knowledge we have concerning them. 



The east border of the highlands overlooks the 

 great Colorado Depression and its outline is composed 

 of irregular escarpments and indented by narrow val- 

 leys which cut into its outline on that side. Its west- 

 ern portion descends by stair-like benches and terraces 

 towards the sea, ending at its borders in wide benches 

 and picturesque cliffs and is attended in places by 

 short, island-like, parallel ranges. The latter are not 

 the Coast Ranges of Northern California, but dis- 

 tinctly fault hills, each a physiographic unit within 

 itself, such as the San Pedro, San Joaquin, San Onofre, 

 and Point Loma Hills. 



VARIOUS FEATURES OF THE NORTHERN END 



The Peninsula Ranges terminate to the north along 

 an east-west cross section through San Gorgonio 

 Pass, via Redlands, Colton, the north side of the Jurupa 

 Mountains (north of Riverside) and the Santa Ana 

 Pass of the Santa Ana River. In a general way the 



'Hanna, Marcus A. Geology of the La Jolla Quadrangle. Geological 

 Bulletin of the University of California. Vol. 16, No. 7, Berkeley, 1926. 



