130 



sand in the El Segundo Sand Hills. Several geologists who 

 have studied the sand dunes have concluded that they might be 

 the result of offshore bar migrationo 



The above discussion is sufficient to indicate that con- 

 siderable changes in the deposit ional history of the bay have 

 taken place, and that on the whole, the rate has decreased in 

 historic time. The changes are attributed largely to alterations 

 in the tributary drainage areas and to the work of man, but 

 climatic changes may in part be responsible for the decrease in 

 the rate of depositiono 



Deposition in the Past Two Decades 



A comparison of Shepard and MacDonald*s samples with 

 those collected by the Hancock Foundation reveal that nearly 

 all of the samples collected in the 1934-38 period or earlier 

 were coarser-grained than those obtained approximately 22 

 years later. There are several possible explanations for 

 this? (1) Shepard and MacDonald used a pipe dredge to collect 

 their samples and some of the finer sediments may have washed 

 out during the dredging operation. Dr. Shepard (personal 

 communication) reports that a piece of cloth was used over 

 one end of the dredge, and that once the dredge was full little 

 washing took place. (2) The mechanical analyses made by both 

 collectors were different. The samples collected by Shepard 

 and MacDonald and the Hancock Foundation used standard sedi- 

 mentary techniques. However, the Emery settling tube was 

 used to analyze the coarse sediments at Hancock Foundation, 

 whereas the earlier samples were analyzed using screens. The 



