and highest adjacent to the Big Slough course, and it thins and slopes away 

 into the adjacent interdistributary and marsh areas. 



The final principal geologic entities in the Brazoria Refuge are coastal 

 salt, brackish, and fresh marshes and associated coastal lakes. The substrate 

 units developed by low-energy shallow-water deposition in modern time (last 

 1,000 yr) and, to an extent, overlap the subsiding margin of the coastal inter- 

 distributary area. The low-lying coastal area is protected from wave activity 

 and circulating currents by Follet's and Galveston Islands. The entire Brazoria 

 Refuge, with the exception of levees adjacent to Big Slough, lies less than 

 1.5 m (5 ft) above sea level. 



Soils and Topography . Topography on the Brazoria Refuge ranges from nearly 

 level to gently undulating, especially near Big Slough. The land slopes slowly 

 but steadily toward the coastline. Slope gradients on both refuges are generally 

 less than five percent and frequently much less. Highest surface elevations 

 on the Brazoria Refuge approach 3 m (10 ft); however, 75 percent of the refuge 

 is less than 1.25 m (4 ft) above mean sea level. These features are the 

 scattered natural ridges found along the Big Slough drainage. Numerous shallow 

 depressions pond surface waters, forming Salt, Nicks, Wolf, and Cox Lakes. 



Much of the San Bernard Refuge is low-lying coastal flats, with approxi- 

 mately 80 percent of its area lying near the 1.5-m (5-ft) contour. The higher 

 3-m (10-ft) sites exist along the northern boundary. A broad shallow central 

 depression collects and channels surface flow inward toward a complex of small 

 lakes, ponds, and potholes called Cow Trap Lake. 



The soils represented in the Brazoria Refuge are of the Harris-Morey- 

 Clodine soil association. The Clodine series loam typifies the upland inter- 

 distributary area and the Harris series predominates (in the Soil Conservation 

 Service classification) in the low coastal marshland (USDA, 1973). 



The surficial soils represented in the San Bernard Refuge area are the 

 result of recent sedimentation associated with channel, delta flood basin, and 

 delta (interdistributary) plain environments. They include the Harris-Morey- 

 Clodine (HMC) soil association, the Pledger-Miller (PM) association, and the 

 Miller-Pledger (MP) association. 



The HMC soil association covers most of the area. The Harris series 

 contains fine silt and montmorillonitic clay typifying level coastal marshland 

 less than 1.5 m (5 ft) above sea level and formed in saline clayey coastal 

 sediments. The Morey series consists of poorly drained acidic soils with a 

 light silty clay loam subsoil developed from alkaline to calcareous dry and 

 silty sediment. The Clodine series contains coarse-grained siliceous loam 

 developed on upland areas and typifying broad, nearly level coastal prairies. 



Both PM and MP soil associations occur along the southwestern border of 

 the refuge, flanking the San Bernard River. Coastward, the Miller series 

 predominates with reddish clays formed in subaerial alluvium of low-level 



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