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Range DescriptionThe range of this species is unclear due to taxonomic uncertainty with the Pacific Drainage members of this genus. In the broadest view, it once ranged from southern British Columbia south to northernmost Baja California, eastward to western Wyoming, eastern Arizona and Chihuahua (Mexico), but this distribution probably includes records for other species (Taylor 1981, Nedeau et al. 2005) such as Anodonta nuttalliana. Taylor (1987) lists the species in 4 inch or greater depth pools in a spring complex above the North Fork of the East Fork of the Black River, Apache Co., Arizona. Clarke and Hovingh (1993) state that "as presently understood this species occurs in California, Nevada, Utah, and Arizona." and that the closely related Anodonta nuttalliana occurs in Oregon, Washington, and British Columbia. Preliminary analysis (K. Mock pers. comm. 2010) indicates Utah Anodonta are distinct from Anodonta oregonensis of the Pacific northwest and should tentatively be assigned to Anodonta californiensis pending future taxonomic work. Presently, Frest and Johannes (1995) report that the range has been reduced and extant populations are currently found in the following areas: the Middle Snake River in Idaho; the Fall and Pit rivers in Shasta County, California; the Okanogan river in Chelan County, Washington; and Roosevelt and Curlew lakes in Ferry County, Washington. No living specimens were found in the Willamette and lower Columbia rivers in searches by Frest and Johannes conducted from 1988-1990. Taylor (1981) reports that most of the natural populations in California have been eradicated and it is probably extinct in most of the Central Valley of southern California. In Utah, the only recent records are in two widely-spaced locations, Big Creek and Reddin Spring pond, but it may still be extant in the Raft River and portions of the Bear River drainage (Clarke and Hovingh 1993). It is extirpated from Utah Lake. Hovingh (2004) found it widely distributed in the Humboldt River drainage (Lahontan Basin) in northern Nevada, in the Bonneville Basin in Utah, Nevada, and Wyoming, and in the Malheur and Warner Basins in Oregon. Mock et al. (2005) list six sites in the Bonneville basin of Utah tentatively assigned to this species.