190 



Sediments 



200 



KILOMETERS 



Figure 162. Distribution of 

 chief heavy minerals along the 

 coast as compiled from various 

 sources given in text. 



that are markedly concave upward in profile 

 have the finest sand near the low-tide level, 

 as though it had been winnowed out of the 

 upper foreshore. As pointed out by Bascom 

 (1951) the transverse variation of grain size 

 requires a standardized sampling point in 

 order to compare the characteristics of dif- 



ferent beaches. The midtide level seems to 

 be the most suitable place for collecting 

 single samples because it is somewhat less 

 subject to change of slope and of grain size 

 than other portions. Analysis of many 

 samples from that point by Bascom clearly 

 shows a parallelism between coarseness of 



SUBMARINE CANYONS 



Figure 163. General characteristics of sand beaches from near Point Conception to Mexico based on observations 

 and samples at approximately 5-mile (8 km) intervals during November 22-24, 1956 (Fig. 28). Top strip shows cumu- 

 lative grain-size distribution of samples. Other strips show median diameter of sediment, width of beach, and esti- 

 mated percentage of shore between sample localities that consists of sandy beach. The notation "fill" indicates areas 

 where slight-to-large widening of the beach has occurred by artificial means, mostly by dredging the floors of adjacent 

 bays. 



