First thing you might want to check out is this exhaustive study done on beaver in California.
The Status of Beaver in California. 1942 by Donald T. Tappe
This is a very useful and informative paper. There is much info to be gleaned from it. But it has been the dominant document coloring people's notion about the historic range of beaver in California and in many ways entrenched the idea of "non-native" beaver in California. In addition this paper supports the idea of multiple geographic species/subspecies of beaver and this view has since been called into question.
Following from the dominant theories espoused in the paper above we have situations like the one documented in the very pertinent paper Management by Assertion: Beavers and Songbirds at Lake Skinner (Riverside County, California) 2006.
But as you may well be aware there are many lines of evidence calling for a reappraisal of the historic range of beaver. Richard Lanman and others have provided compelling evidence for the historic presence of beaver into the high sierra nevada. Much of the information is reviewed here in A Reassessment of the Historical Range of Beaver and Implications for Salmonids. If you want to go further chick out Beaver in the Sierra Nevada and the papers by Richard: Novel Physical Evidence Beaver were Historically Native to the Sierra and The Historical Range of Beaver in the Sierra: A Review of the Evidence can both both be googled and pdfs downloaded for free on the Internet.
|Sherry & Ted Guzzi. Blackwood Creek. Sierra Nevada|
Now to tie it all together, why beaver were once extant but then largely exterminated in California, you need to look at the California Fur Rush wiki page. This lays it all out, the motive behind British/Russian fur trappers to create a "fur desert" to deter American westward expansion. A little thing called gold changed all of that. But by the time naturalists started documenting animals of California they were not seeing beaver or only small relict populations due to the blitzkrieg that preceded them.
The story of beaver in California is a compelling one and one not yet finished.
|(c) CA water institute|
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