When considering the history of bird use within the GSL region, it is important to consider its climate and geomorphic history. The GSL is a recent lake, dating approximately 10,000 years before present (YBP). Its Pleistocene predecessor, Lake Bonneville, with its enormous size, abundant fresh water, and cool climate, was significantly different from today’s GSL. Avian paleontological evidence indicates that Bonneville supported, in part, a different avifauna complex than what currently persists in this more arid climate (Miller 2002).

Between 19,000-10,000 YBP the climate changed and a catastrophic hydraulic breaching of weaker geologic substrate at Red Rock Pass spilled 105 vertical meters of water from Lake Bonneville into the Columbia River Basin. These events soon led to a salt lake environment.  Much paleoclimatic evidence indicates two periods of aridity occurred during the mid-Holocene Epoch. These periods were between 7,500 and 5,000 years ago (Street and Grover, 1979). Evidence suggests that the GSL was a playa landscape, at least briefly, during mid-Holocene time (Currey 1980). Even in the absence of a salt water body, salt marshes and saline ponds would have existed especially along the near-mountain, east margins of the lake basin. This is important when considering the potential history of long-term waterbird presence in the area during profound periods of dryness.