4 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 27 



In the laboratory the tapes of continuously recorded soundings were 

 reduced to half scale with a pantograph and the reductions were traced 

 directly for Figures 3 through 15. U.S. Coast and Geodetic Survey 

 navigational charts served as the source for contours of the index map 

 for each of the canyons. 



Characteristics 

 General: — The canyons off southern California have been described 

 previously by Shepard and Emery (1941) and by Emery (1960a) who 

 also summarized the pertinent literature on them. Accordingly, only new 

 data on topography and data needed for the proper interpretation of 

 water characteristics and sediments will be presented here. 



The canyons occupy parts of three physiographic environments of 

 the sea floor: continental or insular shelf, basin slope, and basin floor. 

 In each environment the canyons present a different aspect. 



Shelf Portion: — The shelf is largely or entirely crossed by 8 of the 

 13 canyons of this study. Santa Monica, San Pedro, and Coronado 

 canyons only indent the shelf ; however, filled extensions of all three 

 canyons are known on the adjacent land through well borings, and a 

 filled channel across the shelf from the head of San Pedro Sea Valley 

 was discovered by jet borings made by Richfield Oil Company. The 

 other two exceptions are Tanner Canyon which begins deep on the 

 saddle between Cortes and Tanner banks, and San Clemente Rift 

 Valley which is different in many ways from other submarine canyons. 

 Among the 8 canyons which do cross most of the shelf, Hueneme, Re- 

 dondo, and Newport have now-filled extensions on land, as shown 

 again by well borings. Each of the 8 also lies off a prominent land 

 valley, except Santa Cruz Canyon which heads into the shelf saddle 

 between Santa Cruz and Santa Rosa islands. Hueneme, Redondo, New- 

 port, La Jolla, Santa Cruz, and Santa Catalina extend in nearly straight 

 courses across the shelves, but Mugu and Dume are broadly curved. 



The depth of the canyon edge, or lip, is not uniform across the 

 shelves. Transverse profiles across the shelf portions of Hueneme, Mugu, 

 Santa Monica, Redondo, San Pedro, Newport, La Jolla, Coronado, and 

 Santa Catalina canyons (see Figs. 3-15) show a seaward deepening of 

 the canyon edge. This deepening is somewhat greater than the general 

 slope of the shelf and, moreover, the profiles show some lateral slope of 

 the shelf toward the canyons. Both facts mean that the topographic 

 effect of the canyons extends somewhat beyond the narrow gorge of the 

 canyons. 



