The habitat of Giant Kangaroo Rats consists of gently sloping and level piedmont plains and (formerly) areas supporting saltbush and perennial grasses; habitat now is dominated by introduced annuals, with many shrubs in some areas. The species occupies areas of sparse vegetative cover and well-drained soils and slope generally less than 9% (Williams and Kilburn 1991) (sometimes up to 22%; USFWS 1998), often in areas that are heavily grazed by cattle and sheep (Williams and Kilburn 1991). They prefer semi-arid slopes at the head of draws in barren shrubless areas, with loose, easily diggable, sandy loam soils. Found in underground burrows when inactive. They are absent from areas continuously in dry-land cultivation and from irrigated fields but may recolonize fallow dry-land grain fields if there are colonies on uncultivated land nearby (Williams and Kilburn 1991). Habitats listed in order of decreasing favorability: 1) annual grassland association in areas with less than five to six inches annual rain, and level to gently sloping ground, 2) alkali desert scrub association in areas with less than five to six inches annual rain, sandy loam soils, and level to gently sloping ground, 3) friable soils of sand, loam, clay loam or gravelly in areas with the above characteristics, and 4) slopes of 10-15 degrees with the above characteristics and located near colonies in more favorable habitats (D. Williams pers. comm).

Home range is about 60-350 m². This species is basically solitary and territorial, with strict intrasexual avoidance indicated. In spring, areas around occupied burrows have a more lush growth of herbaceous vegetation than do areas between burrow systems; this growth is eventually removed by grazing by livestock and/or kangaroo rats (Williams and Kilburn 1991). Digging and feeding activity promote the establishment of exotic weeds, which in turn are a favoured food source (Schiffman 1994). Giant Kangaroo Rats feed on seeds, especially those of Lepidium nitidum, oenothera, Bromus rubens, and Erodium cicutarium. They also eat some green herbaceous vegetation and occasionally insects. In some localities. They gather dry grass into "haystacks" to cure, later removing seeds for storage in underground burrows. They also temporarily bury seeds in the ground before storing in burrows. Giant Kangaroo Rats emerge to forage soon after sunset in spring. They spend a little less than two hours per night above ground actively foraging in spring-summer (Braun 1985).

Limited data indicate that the reproductive season may extend from January through May (Williams and Kilburn 1991) (February to June or perhaps later according to Biosystems Analysis 1989). Gestation lasts about one month. Litter size is three to six (Biosystems Analysis 1989); average litter size is probably four (Williams and Kilburn 1991). Young are weaned at four weeks (Matthews and Moseley 1990).

The species is endemic to California in the United States where it is confined to a narrow strip along the southwestern border of the San Joaquin Valley and a few nearby valleys to the west, including the Carrizo and Elkhorn plains and upper Cuyama Valley, with scattered colonies in the Ciervo, Kettleman, Panoche, and Turney Hills, and the Panoche Valley (Grinnell 1922, Hall 1981, Williams and Kilburn 1991, Williams et al. 1993). Its historical range extended from Merced County south to the base of the Tehachapi Mountain in Kern County, and west to eastern San Luis Obispo County and extreme northern Santa Barbara County (Williams et al. 1993). Its elevational range extends to about 868 m asl (400-2,850 feet).

The population is currently fragmented into six major geographic units: 1) the Panoche region in western Fresno and eastern San Benito counties; 2) Kettleman Hills in Kings County; 3) San Juan Creek Valley in San Luis Obispo County; 4) western Kern County in the area of the Lokern, Elk Hills, and other uplands around McKittrick, Taft, and Maricopa; 5) Carrizo Plain in eastern San Luis Obispo County; and 6) Cuyama Valley in Santa Barbara and San Luis Obispo counties (see USFWS 1998). These major units are fragmented into more than 100 smaller subpopulations, many of which are isolated by several miles of barriers such as steep terrain with plant communities unsuitable as habitat, or agricultural, industrial, or urban land without habitat for this species (USFWS 1998).

This rodent occurs in several protected areas (D. Tirira pers. comm).