The reservoir has a capacity of 197,756 acre⋅ft (243,928,000 m3) and is formed by Twitchell Dam on the Cuyama River about 66 miles (106 km) from its headwaters in the Chumash Wilderness Area.

The Central Coast of California only receives significant amounts of rainfall during the winter, this area averaging 14 inches (360 mm) per year.

The water is stored in the reservoir during big winter storms and released as quickly as possible while still allowing it to percolate into the soil and recharge the groundwater.

This reduces its capacity and blocks the water inlet to the control gates.

Some sediment has been removed by flushing it out during releases, but much of it is simply deposited immediately downstream, interfering with flows.