# # National Water Information System # 2024/11/21 # # # Date Retrieved: USGS Water Data for the Nation Help System # gw_ref_cd gw_ref_nm gw_ref_ds 1s 16s 102s A Alluvial fan Stream deposit of loose rock material where it issues from a narrow mountain valley upon a plain. B Playa Undrained desert basin in which water accumulates and is quickly evaporated. C Stream channel Bed in which a natural stream of water runs. D Local depression An area that has no external surface drainage. E Dunes Mounds and ridges of windblown, or eolian sand. F Flat surface May be part of a larger feature, such as a plateau, plain, or pediment. G Flood plain Smooth land surface adjacent to a river channel that is flooded when the river overflows its banks. H Hilltop Upper part of a hill or ridge above a well-defined break in slope. K Sinkhole Depression that results from the dissolving of soluble rocks and collapse into the solution cavity. L Lake or Swamp Inland lake, swamp, or marsh where the ground may be saturated or water stands above the land surface. M Mangrove swamp Tropical or subtropical marine swamp characterized by abundant mangrove trees. O Offshore Site along a coast or estuary that is continuously submerged. P Pediment Plain of combined erosion and deposition that forms at the foot of a mountain range. S Hillside Sloping side of hill, the area between the hilltop and valley flat. T Alluvial terrace Generally a flat surface, usually parallel to but elevated above a stream valley or coast line. U Undulating Topography is characteristic of areas which have many small depressions and low mounds. V Valley flat Low flat area between the valley walls and bordering a stream channel. W Upland draw Small natural drainageway