Boundaries

This ecoregion corresponds to the Bonneville Basin, the single largest interior drainage in the Great Basin (Minckley et al. 1986). The ecoregion occupies much of western Utah with extensions into eastern Nevada, southeastern Idaho and a small portion of southwestern Wyoming. The Butte Mountains and Pequop Mountains constitute the western boundary of this ecoregion, while in Utah the eastern boundary lies to the west of the Wasatch Plateau and north of Dixie National Forest.

Topography

This ecoregion forms part of the Great Basin, which is comprised of isolated north-south trending mountain ranges and valleys known as the Basin and Ridge Province. Elevation ranges from 4,000 to 8,000 ft (1,200 to 2,400 m) (McNab and Avers 1994).

Freshwater habitats

The Bonneville Basin was formerly Lake Bonneville, a large freshwater sea during the Pleistocene. Today Great Salt, Utah, and Sevier lakes are desert remnants of the former Lake Bonneville. The Great Salt Lake is the largest of these, with salinity levels that do not support fish, except near inflows of tributaries. Sevier Lake is ephemeral and when filled also is highly saline. The waters of Utah Lake, however, are relatively fresh and support fish species (Minckley et al. 1986).

Terrestrial habitats

Most of the ecoregion is comprised of shrub steppe, with dominant species including distinctly cold-temperate sagebrushes (Artemisia), saltbrushes (Atriplex), and winterfat (Ceratoides lanata) (Turner 1994). Coniferous forests are the dominant vegetation at the eastern edge of the ecoregion. 

Description of endemic fishes

Much of the Bonneville’s distinctive biodiversity is harbored in its lakes. Bear Lake, located high in the mountains near the border of Utah, Idaho, and Wyoming, has four endemic fish species, all remnants of the Pleistocene-era Lake Bonneville fauna—the Bear Lake sculpin (Cottus extensus), Bear Lake whitefish (Prosopium abyssicola), Bonneville whitefish (P. spilonotus), and Bonneville cisco (P. gemmiferum). Utah Lake, located southeast of the Great Salt Lake and distinguished as the largest freshwater lake west of the Mississippi, historically supported two endemic fish, also Lake Bonneville remnants. These are the June sucker (Chasmistes liorus), found also in the lake’s tributaries, and the now-extinct Utah Lake sculpin (Cottus echinatus). The Bonneville Basin shares the leatherside chub (Gila copei) and the Utah sucker (Catostomus ardens) with the Upper Snake ecoregion [122], but the species can be considered endemic to both ecoregions. Finally, the Bonneville is home to two subspecies of speckled dace (Rhinichthys osculus adobe and R. o. carringtoni), as well as the endemic least chub (Iotichthys phlegethontis), historically found in the Great Salt Lake marshes and in streams along the Wasatch Front (Minckley et al. 1986; Sigler & Sigler 1994). 

Justification for delineation

Ecoregion boundaries are taken from Abell et al. (2000) and are based on subregions defined by Maxwell et al. (1995).