shell comprise the remainder. The average of the mean grain size for 

 samples at 30 feet in Area C is 2.5<J> (.176 millimeters). 



Sediments at the 30-foot depth near Area B consist of light brownish 

 gray (2.5Y6/2), fine grained quartz sand. The sand is composed of ap- 

 proximately 85 percent subangular to angular quartz grains (roundness 0.3, 

 sphericity 0.7). The remainder (about 15 percent) is composed of meta- 

 morphics and heavy minerals with minor traces of shell. Average grain 

 size for samples in this area is 2.564) (.173 millimeters). 



Sediments at the 30-foot depth near Area A consists of olive gray 

 (5Y5/2), fine grained quartz sand. The sand is composed of 80 to 90 per- 

 cent angular quartz grains (roundness 0.2, sphericity 0.7). The remainder 

 is composed of 10 to 20 percent metamorphics and heavy minerals. The 

 average grain size for samples at 30-foot depths in this area is 2.3<i> 

 (.203 millimeters). In Area A, a marked decrease in size is noted eastward 

 along the 30-foot depth contour. A more detailed analysis of sediments 

 in these areas (C, B, and A) is given in Appendix E. 



In the spring and summer, brisk north and northwest winds are common 

 along the west coast of the United States. These winds serve to drive the 

 southward-flowing California Current close inshore along the California 

 Coast. During the fall and winter, a north-directed surface current, the 

 Davidson Current or California Countercurrent , develops inshore off Lower 

 California, Mexico, and may extend to i+5°N (Wright, 1967 ) . Since this 

 includes the latitudes of the present study, these currents could affect 

 patterns of sediment movement, although such an effect has not yet been 

 demonstrated. 



Average wave conditions for survey periods are given in Table III 

 along with computations for bottom orbital velocity and calculated sedi- 

 ment migration rate. Figures 38 through U3 illustrate these wave con- 

 ditions. From Table III it may be seen that the bottom orbital velocity 

 is sufficient to place sand in suspension and thus induce sand movement. 

 It is then approximated that the sand should move forward at the rates 

 given by 1/3 the wave drift veloctiy (u) (Bagnold, 19^7) and (Vernon, 1965). 

 Sediment transport values for each of the areas around Point Conception 

 are summarized by Table III. Velocities required for transport of the 

 average particle are derived from -Hjulstrom' s suspension curve given in 

 Heezen and hollister (196U). An approximation of the average bottom 

 current based on grain size is given using the method described by Wilde 

 (1965) where U = w/a in which U = bottom current, w = settling velocity 

 of mean grain, and a is the bottom slope. 



53 



