 Much of the plains region is semiarid, with steady winds that hasten evaporation of surface water and precipitation.In many locations, the aquifer is overlain, in the vadose zone, with a shallow layer of caliche that is practically impermeable; this limits the amount of water able to recharge the aquifer from the land surface.However, the soil of the playa lakes is different and not lined with caliche, making these some of the few areas where the aquifer can recharge.