File:Soda Lake, Carrizo Plain National Monument, California (20961558643).jpg

Soda Lake is a shallow, ephemeral, alkali endorheic lake in the Carrizo Plain in southeastern San Luis Obispo County, California. The lake is located on the southwest side of the northern Carrizo Plain, 103 km (64 mi) east of San Luis Obispo. It can be reached by Soda Lake Road, which runs northwest–southeast between State Route 166 and State Route 58. The lake is at an elevation of 580 m (1,900 ft) and covers an area of about 12 km2 (4.6 sq mi).

Internal drainage of the Carrizo Plain and the formation of Soda Lake began during Pliocene-Pleistocene time when tectonic deformation associated with the San Andreas Fault defeated a stream that once drained the valley. An originally fresh to brackish water lake probably persisted through much of the Pleistocene during which coastal California was wetter and cooler than now. Diminished Holocene precipitation and a higher evaporation rate led to shrinkage of the ancestral lake and associated increased salinity which set the stage for clay dune formation.

The largest dune bounds the eastern and southern edges of the northern basin. This dune is up to 470 m wide, 16.7 m high, and nearly 9.5 km in length. Part of the dune is active, receiving sediment from the mud flat exposed between the dune and the salt pan. Most of the eastern (north-south) leg of the dune, which is lower and narrower, is currently inactive. Westward retreat of the shoreline exposed the former lake flat to colonization and stabilization by salt-resistant plants.

en.wikipedia.org/wiki/Soda_Lake_(San_Luis_Obispo_County)