Sevier Lake. Sevier Lake today is a playa lake, one that collects water in colder and wetter seasons, but dries up in warmer seasons. The evaporating water leaves behind vast stretches of salt flats. Erosion strips down the mountains, and carries sediments down to the valleys creating alluvial fans. These spread out from the canyons down to the valley floors and along with playa lakes, are classic geologic features of basin and range topography. Eventually the sediments are carried to the floor of the valleys, where they have accumulated in layers thousands of feet thick.