Lonesome Lake is an ephemeral wetland surrounded by native shortgrass prairie. The lake is fed by spring runoff from three coulees. The IBA is a mix of BLM land and privately owned ranchland, with the BLM land being managed to provide habitat for wildlife dependent on shortgrass prairie. Legal description for the IBA is T29N, R11E, sects. 10-15 & 24; T29N, R12E, sects. 7-10, 15-22, & 27-30.
Volunteers from Upper Missouri Breaks Audubon have documented more than 100 species of birds on the IBA. The grasslands support a large number of nesting species of Global and Continental conservation concern, including Ferruginous Hawks, Northern Harriers, Long-billed Curlews, Upland Sandpipers, Burrowing Owls, Short-eared Owls, Sprague's Pipits, Loggerhead Shrikes, Baird's Sparrows, Chestnut-collared Longspurs, and McCown's Longspurs. Waterfowl are common in wet years but virtually absent during drought years, when the lake is dry.
Overgrazing by cattle has degraded wetland and upland habitats. Agriculture has been expanding on private lands, creating a net loss of native grasslands. The lake is without water during prolonged periods of drought, when the area becomes unsuitable for use by waterfowl and other wetland-dependent species.
Of the 23 sections of land within the IBA, the BLM owns about 16.5 sections, the state of Montana about 2.5 sections, and the remaining 4 sections are private ranchlands.
The majority of the IBA is native prairie, with the remainder consisting of an ephemeral lake and some rather intensively farmed (dryland) private land.