IV-57 



counties which comprise the basic political subdivisions of the 

 estuarlne zone. These coastal counties form a strip of land 

 averaging about 50 miles wide along the coast, except where the 

 large embayments of the Chesapeake Bay and Puget Sound make this 

 strip reach more than 100 miles from the ocean. 



The total area of the coastal counties 1s 552,000 square miles 

 with the bulk of this 1n the Alaskan estuarlne region and the 

 smallest part 1n the Pacific Island estuarlne region. In the 

 Middle Atlantic, South Atlantic, and Gulf regions, the coastal 

 strip Is a low-lying plain composed of easily erodable materials 

 which tend to be deposited 1n the estuarlne zone and moved about 

 by waves and currents. The ocean coast 1s mostly sand throughout 

 these regions, overlain near river mouths by some mud and clay. 

 The Mississippi delta is entirely mud, clay, silt, and sand washed 

 down from the heartland of the continent. Sand, mud, and clay 

 predominate in the embayments, with sand characteristic of open 

 waters and mud common in marshes. 



Rock, gravel, and sand are the common bottom materials along the 

 North Atlantic coast, with the rock overlain by fine mud and silt 

 1n confined areas and sand common 1n the offshore areas. 



The Pacific coast counties form mountainous strips along the 

 coast. Sediments reaching the ocean in this region tend to be 

 deposited in broad tidal flats or bars where currents permit, or 

 washed off Into the ocean where wind and waves motion is suffi- 



