A limnogeological expedition examined the sedimentary record of Lake Urmia, one of the world's largest saline lakes, located in a tectonically active, arid, intermontane plateau in northwestern Iran, near the cradle of western civilization. Lake Urmia resembles the Great Salt Lake, U.S.A. in many respects of morphology, water chemistry, and sediments. The present lake area is about 5000 km 2, shallow (8–12 m), and a perennial sodium chloride—sulfate system (22% salts). High resolution (3.5 kHz) seismic profiles show morphological relicts from a desiccation playa phase buried below only a few meters of sediments from lacustral phases. In places, around the deeper areas, the lake floor is not smooth but covered with mounds aligned in prevailing current directions. These are erosional relicts rather than bioherms. Sediments comprise aragonite chemical precipitates, fecal-pellet sands, detrital clayey muds, thin aragonite crusts, oolites, various gypsum types and occurrences of dolomite in peripheral areas. Organic matter, characteristic of the present shorelines, is not preserved at depth in basinal areas. Piston cores up to 6 m long penetrated a Holocene sequence of hypersaline facies with laminated aragonite—fecal-pellet muds and bottomed in a playa—mudflat facies with central gypsiferous muds and marginal terrigenous to dolomitic muds. Preliminary radiocarbon and pollen analyses suggest a playa stage prior to 9000 yr B.P. with saline lake deposition in a cool arid climate. From 9000 to 7500 yr B.P., higher-energy facies prevailed in a shallow saline lake and, since then, present-day saline environments have persisted with evidence of numerous second-order water-level fluctuations. The preliminary results suggest a lake system out-of-phase with North African and some other Middle Eastern lakes.