36 



Physiography 



FLATROCK POINT 



Figure 37. Contour map of Palos Verdes Hills and adjacent sea floor at contour interval of 100 feet. Note that this 

 interval fails to reveal any except the widest raised terraces; in contrast is the great width of the mainland shelf, a com- 

 posite of several terraces of slightly diff"ering depths. Smoothly curving contours of basin slope beyond the shelf-break 

 are partly due to the relative scarcity of sounding data on sea floor as compared to elevation data on land. 



on the sea floor indicate much diastrophic 

 movement suggest that the shelf terraces 

 are younger than those of diastrophic origin. 

 At Ventura (Putnam, 1942) the high terraces 

 bevel strata that were folded during the mid- 

 Pleistocene diastrophism, and at Palos Ver- 

 des Hills (Woodring, Bramlette, and Kew, 

 1946) fossils in marine deposits on the ter- 

 races indicate a Middle or Late Pleistocene 

 date. In addition, stream channels cut as 

 much as 230 feet below sea level at the pres- 

 ent shoreUne must have been correlative with 

 the submerged terraces; these channels are 

 eroded into Early and Middle Pleistocene 

 strata in the Ventura and Los Angeles Basins 

 and have been filled by later sediments (Up- 



son, 1949; Crowell, 1952; Poland, Piper, and 

 others, 1956). Thus, several hues of evidence 

 indicate that at least in part of the area off 

 southern California the submerged terraces 

 are no older than Middle Pleistocene. Per- 

 haps they were cut during the eustatic levels 

 of the Wisconsin Age that correlate with the 

 lowan, Tazewell, Gary, and Mankato Sub- 

 ages (Fhnt, 1947, p. 212). In the Sierra 

 Nevada also, several separate Wisconsin 

 moraines probably are correlative with sep- 

 arate terraces of Mono Lake (Putnam, 1950). 

 Several diff'erent eustatic sea levels have been 

 suggested by Zeuner (Ericson and WoUin, 

 1 956b) for subages of the Wisconsin. Thus, 

 it is possible that the broad gently sloping 



