40 



Physiography 



STATUTE MILES 



Figure 40. Comparison of sev- 

 eral basin slopes at various 

 distances from shore. Note 

 that the base of some slopes is 

 bordered by a trench and others 

 by an apron. Still other slopes 

 have intermediate kinds of 

 bases. Vertical exaggeration — 

 X5. 



detected by fathograms run parallel to the 

 slope. The smallest of these features have 

 been termed sea gullies by Buffington (1951), 

 who found them on slopes between San 

 Diego and San Pedro. Subsequently they 

 have been found on nearly every slope 

 studied. Good examples exist off the Palos 

 Verdes Hills where each sea gully was crossed 

 by several fathograms (Fig. 43). Although 

 not definitely established, it is believed by 

 Emery and Terry (1956) that the sea gullies 

 are elongate landslide scars produced by 

 movement of sediment down the slope to 

 the apron at the bottom. Cores in the slope 

 encountered nothing but sediment, and the 

 sea gullies have side slopes of the same 

 steepness as the front of the basin slope into 

 which they are incised. 



Submarine canyons also cross the slopes 

 and parts of the adjoining shelves. These 

 features are much larger and more complex 

 than the sea gullies and will be discussed 

 separately in the following section. 



Submarine Canyons 



Characteristics 



There are few physiographic features of 

 the world about which more papers have 

 been written and yet less is known regarding 

 origin than submarine canyons. Nearly all 

 that is known about them has been learned 

 during the past 25 years. The effort to 

 secure facts was headed by Shepard, who 

 studied the California canyons principally, 



