The Fort Rock Basin is an endorheic basin. Increased moisture in this semiarid environment during the Pleistocene through increased cloud cover and cooler temperatures resulted in higher lake levels. At its maximum, the lake filled the basin up to 75 m deep (245 ft), with a surface area of over 2,300 km2 (900 mi2). While this is larger than any modern lakes in Oregon, Paleolake Fort Rock was smaller than any of the other paleolakes to the south.