North side: 49 cubic meters 



East side: No significant accumulation. 



Total: 1,597 cubic meters 



These figures apply only to the talus beds shown in Figures 9 to 

 12. The talus beds extended around the southwest and northwest wings 

 of the island and contained a large volume of shell debris. At the 

 west edge of each of these wings, talus beds were of dimensions 

 similar to those lying along the west side. The beds diminished 

 markedly on the flanks of the southwest and northwest wings where 

 they adjoin the south and north sides, respectively, of the island. 

 No significant shell talus acciamulations were observed around the 

 base of either the northeast or the southeast wing. 



The west-side talus beds, averaging 16.5 cubic meters per meter 

 of lineal distance along the west revetment, were considerably more 

 voluminous and extensive than the beds on the other sides. This is 

 because the tetrapods on the west side supported a very heavy growth 

 of mussels (Mytilus calif ornianus) in the intertidal zone. Parts of 

 this are sometimes removed by heavy surf, which is most pronounced on 

 the west (seaward) side. Some of the detached mussels gravitate into 

 quarry rock and tetrapod interstices, but many accumulate at the foot 

 of the revetments. 



West-side talus beds were composed almost entirely of mussel 

 shells, many of which were of unusually large size for this species. 

 Paine (1976) reported a specimen of W. calif ornianus exceeding 26.6 

 centimeters in length from a subtidal mussel bed on Duncan Rock off 

 Washington. The previous record was 25.1 centimeters, as reported by 

 Chan (1973). A mussel measuring 25 centimeters has been reported at 

 an offshore oil platform in southern California (Southern California 

 Coastal Water Research Project, 1976). Although no measurements were 

 taken on shells in the Rincon Island talus bed, many specimens appar- 

 ently approaching this size were observed. Some shells of Pododesmus 

 cepio were also present in the west-side talus area. The seaward 

 boundary of the west-side talus bed (where it graded into natural 

 sedimentary bottom) was very distinct and lacking in irregularities. 

 The inner margin was somewhat irregular and interspersed with iso- 

 lated rocks. Isolated pockets of talus existed above the upper 

 margin of the main talus bed. 



In contrast, the east side was nearly devoid of shell talus. 

 Only one pocket 'of talus was observed, approximately 4 meters from 

 the south boundary of the side. Small mounds of mussel shells were 

 observed at the bases of causeway pilings. The east side is the most 

 sheltered side, and appears to act as a deposition site for sediment 

 carried to the rear of the island in turbulent eddies (Keith and 

 Skjei, 1974). The middepth and deeper parts of the east-side re- 

 vetments were always overlain by a veneer of fine sediment: the 



38 



