The Alkali Lakes are a series of three large playas located in the Surprise Valley of northeastern California, United States.

The lakes lie at the bottom of a graben created by the Surprise Valley Fault, which has experienced nearly a mile (1.6 km) of vertical displacement, resulting in the steep eastern scarp of the Warner Mountains.

Sediment deposits indicate Lake Lahontan was up to 550 feet (170 m) deep in this area, which would have filled the entire valley.

The valley was named "Surprise" because of the relatively abundant greenery, supported by streams flowing from the Warner Mountains, in stark contrast to the surrounding high desert country.

With growing water use and drought conditions in the 21st century, falling groundwater levels in the basin are an increasing concern.

[6] The lakes form an endorheic (closed) drainage system in the western edge of the Great Basin.

[5] This is enough to flood the lake beds 8 inches (200 mm) deep; however, most of the water is either appropriated for irrigation, or evaporates in the desert heat.