The southeastern part of Arkansas along the Mississippi Alluvial Plain is sometimes called the Arkansas Delta. This region is a flat landscape of rich alluvial soils formed by repeated flooding of the adjacent Mississippi. Farther from the river, in the southeastern part of the state, the Grand Prairie has a more undulating landscape. Both are fertile agricultural areas. The Delta region is bisected by a geological formation known as Crowley's Ridge. A narrow band of rolling hills, Crowley's Ridge rises above the surrounding alluvial plain and underlies many of eastern Arkansas's major towns.