Wind, waves, and currents constantly move and redistribute coastal sediments along shorelines. Beach sediments that have been transported great distances will be sorted according to grain size. For example, Gulf Coast sediments may have traveled the length of the Mississippi River. Winnowing of more uniform sediment shapes and sizes results in a beach with well-sorted sediments. In contrast, poorly sorted sediments are composed of a variety of sediment shapes and sizes. Low-energy conditions that allow fine sediments to settle from suspension must exist for the formation of muddy or sandy beaches. High-energy conditions are typical of rocky beaches that allow for the transportation of coarser sediments. Extreme storm events are necessary to move the largest sediments (i.e., boulders).