The Gulf Prairies and Marshes region is a nearly level, slowly drained plain less than 150 feet in elevation, dissected by streams and rivers flowing into the Gulf of Mexico. The region includes the barrier islands lining the coast which protect the shoreline from the constant buffeting of harsher ocean waves, and the highly productive estuaries and marshes that support a thriving fishing economy. Rainfall varies from 20 to 50 inches per year distributed fairly uniformly throughout the year. The growing season is usually more than 300 days, with high humidity and warm temperatures. Soils on the Gulf Prairies and Marshes are acid sands, sandy loams, and clays.
Sandy loams predominate, with clays occurring in river bottoms.
Post oak savanna or grassland are the major climax vegetation types on the majority of the region. Much of the area has been invaded by trees and brush such as mesquite, prickly pear, oaks, and acacias. Tall bunch grasses are the dominant climax species. These subregions are fairly self explanatory. The dunes and barrier islands define the first, and coastal wetlands comprise the second.