WordNet (r) 3.0 (2006):

salt flat
    n 1: a flat expanse of salt left by the evaporation of a body of
         salt water [syn: salt flat, salt plain]

Moby Thesaurus II by Grady Ward, 1.0:

77 Moby Thesaurus words for "salt flat":
   Arabia Deserta, Death Valley, Sahara, alkali flat, alluvial plain,
   barren, barren land, barrens, basin, bottomland, brush, bush,
   bushveld, campo, champaign, champaign country, coastal plain,
   delta, desert, desolation, down, downs, dust bowl, fell, flat,
   flat country, flatland, flats, grass veld, grassland, heath,
   howling wilderness, karroo, lande, level, llano, lowland, lowlands,
   lunar landscape, lunar mare, lunar waste, mare, mesa, mesilla,
   moor, moorland, open country, outback, pampa, pampas, peneplain,
   plain, plains, plateau, playa, prairie, salt marsh, salt pan,
   savanna, sebkha, steppe, table, tableland, tree veld, tundra,
   upland, vega, veld, waste, wasteland, weald, weary waste,
   wide-open spaces, wild, wilderness, wilds, wold