The town of Fort Bidwell is located at the north end of Upper Alkali Lake. Lake City and Cedarville are located between and west of Upper and Middle Alkali Lakes. Eagleville is situated south of Lower Alkali Lake. California State Route 299 crosses the basin in-between the Upper and Middle lakes. As the crow flies, the lakes are located about east of Alturas and northeast of Redding. The lakes lie at the bottom of a graben created by the Surprise Valley Fault, which has experienced nearly a mile of vertical displacement, resulting in the steep eastern scarp of the Warner Mountains. They are a remnant of Glacial Lake Lahontan, which existed up until about 12,000 years ago during the last Ice Age. Sediment deposits indicate Lake Lahontan was up to deep in this area, which would have filled the entire valley. The surrounding area has been used for agriculture since the first settlers arrived in the 1840s. 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. Salt was extracted from briny wells on the east side of Middle Alkali Lake until 1943.
Hydrology
The lakes form an endorheic drainage system in the western edge of the Great Basin. With a total combined surface area of, the lakes receive runoff from a drainage basin of and are considered part of California's North Lahontan watershed. Despite the nomenclature, the direction of water flow is not from north to south. Middle Alkali Lake is actually the highest at above sea level. Water will either flow south to Lower Alkali Lake at, or north to Upper Alkali Lake at. The lakes are seasonally flooded with alkaline water in most years, drying out in the summer. Annual precipitation in the basin ranges from. The average annual runoff is, which occurs mainly between March and June as snowmelt. This is enough to flood the lake beds deep; however, most of the water is either appropriated for irrigation, or evaporates in the desert heat. Formed by erosion during the Pleistocene, the alluvial deposits that make up the lake beds are up to deep at Middle Alkali Lake and hold significant amounts of groundwater. The Surprise Valley Groundwater Basin has an estimated volume of.
Upper Alkali Lake
The northernmost lake, Upper Alkali Lake has a drainage area of. The lake is fed by Bidwell, Second, Goose, Wilkinson, Mill, Releford and Soldier Creeks, as well as overflow from Middle Alkali Lake if the level of that lake is high enough.
Middle Alkali Lake
Middle Alkali Lake is the largest by both surface area and drainage area. The total catchment of Middle Alkali Lake is. Creeks flowing into the lake include Sand, Fortymile, Cedar, Deep, Granger, Milk, Cottonwood, Owl and Raider Creeks. Between Middle and Lower Alkali Lakes there is a smaller lake called Cambron Lake, fed by Highrock and Eagle Creeks.
Lower Alkali Lake
Lower Alkali Lake is the southernmost and smallest lake, draining. Streams feeding the lake include Emerson, Barber, and Bare Creeks, as well as occasional overflow from Middle Alkali Lake.
