IUCN threat status:

Least Concern (LC)


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Range Description

This species occurs patchily in Pacific drainages in the USA, in the States of California, Oregon, Idaho and Washington (NatureServe 2009). Taylor (1981) lists its distribution as southern Washington to northern and east-central California, and east to the Snake River, southern Idaho. In California, it occurs in the Klamath, upper Sacramento and northeastern interior drainages, and Lake Tahoe. It is possibly extinct in the Owens Valley, Inyo County (Taylor 1981).

Various subspecies exist, although they may need revision (Frest 1999, cited in NatureServe 2009): V. effusa effusa is rare and declining in the Sacremento River system, but widespread in the Willamette River in Oregon, the lower Columbia River in Washington and Oregon, the Snake River and a few tributary springs in Idaho (NatureServe 2009). V. e. dalli (the Dall Rams-horn) and diagonalis (Lined Rams-horn) are restricted to, respectively, four and five sites in the Klamath Lake system, Oregon, where they are listed as species of conservation concern (Brown et al. 2009).


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© International Union for Conservation of Nature and Natural Resources

Source: IUCN

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