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![Polygonal cracks in salt pan.](http://www.scienceiq.com/Images/FactsImages/saltpan.jpg)
The wet times didn't last. The climate warmed and rainfall declined. The lake began to dry up. Minerals dissolved in the lake became increasingly concentrated as water evaporated. Eventually, only a briny soup remained, forming salty pools on the lowest parts of Death Valley's floor. Salts (95% table salt - NaCl) began to crystallize, coating the surface with a thick crust about three to five feet thick.
Here at Badwater, significant rainstorms flood the valley bottom periodically, covering the salt pan with a thin sheet of standing water. Each newly-formed lake doesn't last long though, because the 1.9 inch average rainfall is overwhelmed by a 150-inch annual evaporation rate. This, the nation's greatest evaporation potential, means that even a 12-foot-deep, 30 miles long lake would dry up in a single year! While flooded, some of the salt is dissolved, then is redeposited as clean, sparkling crystals when the water evaporates.