Sea-Floor Topography and 

 Sediment Distribution 



Detailed geological mapping of the 

 sea floor around the tower shows, recent 

 marine sands overlying older deltic 

 sedimentary fill of the San Diego River. 



The sea-floor surface from 

 Mission Beach to the tower is composed 

 of well-sorted, fine-grained gray sand, 

 with a median particle diameter of 0. 09 

 millimeter, and ripple marks approxi- 

 mately 3 to 4 inches high. At the tower, 

 sediments change abruptly. Ripple marks 

 increase to an average height of 6 inches, 

 and sand grain size increases to around 

 0. 31 millimeter. About 1 mile west of 

 the tower the bottom sediment again be- 

 comes finer, ripple marks disappear, 

 and the bottom slope steepens. 



Long-term sea-floor observations 

 around the tower using scuba and televi- 

 sion have identified cyclic variations in 

 ripple mark heights corresponding to 

 seasonal variations in waves, currents, 

 and animal populations. In winter, ripple 

 marks reach a height of approximately 8 

 inches (with wavelengths up to 40 inches) . 

 In summer, they gradually reduce to 2 or 

 3 inches high due to decreasing water 

 motion and increased activity of marine 

 organisms. 



Some 900 feet west of the tower, at 

 a depth of 66 feet, coarse sand 

 ripples measuring 36 inches from 

 crest to crest are in evidence. Their 

 6-inch high peaks show irregular 

 erosion by sand dollars, heart 

 urchins, and sea urchins. Scattered 

 broken shells and a thin layer of 

 organic matter have collected in the 

 troughs. 



