 These two regions are separated by Bayou Bartholomew, the world's longest bayou, which approximately splits the county into eastern and western halves with significant differences in geography.In the east, the Arkansas Delta is a subregion of the Mississippi Alluvial Plain, which is a flat area consisting of rich, fertile sediment deposits from the Mississippi River between Louisiana and Illinois.The western half is part of the Arkansas Timberlands, a portion of the Gulf Coastal Plain characterized by flat pine and cypress forests and silviculture rather than row agriculture.