NO. 1 hartman: quantitative survey 



DESCRIPTION OF THE AREA 



The area selected for a quantitative investigation is the San Pedro 

 Basin (Chart 1), the shallowest of a series of about a dozen depressions 

 along the coast of southern California (see Emery and Shepard, 1945, 

 "Lithology of the sea floor off southern California." Bull. Geol. Soc. 

 America, vol. 56, pp. 431-477, chart). It lies between the mainland of 

 southern California and Catalina Island, and is continuous northwest- 

 ward through a narrow channel with the Santa Monica Basin. It is 

 bounded by a submarine valley, the Redondo Canyon, to the north, and 

 by the city of South Laguna Beach to the south. Its geographic boun- 

 daries extend from 33° 16' to 33° 50' north latitude, and 117° 46' 

 to 118° 36' west longitude. The area comprises about 520 square miles 

 of sea bottom. Depths range from 4 to 495 fathoms, with the deepest 

 measured depth about half way between Isthmus, Catalina Island, and 

 Long Point, on the mainland. There are two poorly marked channels 

 running approximately parallel to the mainland. There is a northwestern 

 threshold or sill depth of about 489 fathoms, only slightly above the 

 deepest part of the basin, and a southeastern one of about 400 fathoms, 

 east of Avalon, Catalina Island. The oceanward basins, beyond San 

 Pedro Basin, gradually attain far greater depths, to more than a thousand 

 fathoms. 



There are four submarine mounts within the Basin, one on each side 

 of the two threshold depths, at the northwestern and southern ends. The 

 largest one, the Lasuen Seamount (Chart 2), is the most easterly. It 

 rises abruptly from 385 to 58 fathoms within a mile. There are steep 

 descents along the rims of Redondo Canyon and along the leeward shores 

 of Catalina Island. There is a broad shallow submarine shelf, about six 

 miles wide at most, south of San Pedro Bay, that extends coastwise from 

 Long Point to Newport Beach. This has an extremely rich and highly 

 diversified fauna. There is a large sewer outlet (conduit for domestic 

 pollution) oflE White's Point, San Pedro, emptying into the sea nearly 

 a mile ollF shore. There are fluvial and terrigenous materials brought in 

 by rivers, especially the Santa Ana River, northwest of Newport Bay, 

 and the San Gabriel River, near Long Beach ; these carry considerable 

 loads into the sea during some months of the year. There is a long break- 

 water at the ocean side of Outer Harbor. There are cable crossings and 

 possible industrial pollutions from manufacturing plants, all of which 

 may have some effect on the productivity of benthic populations. 



