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Earlier , in 1906 , Frank Stephens wrote in " California Mammals " that Castor canadensis ' historic range was from the " Pacific slope from Alaska to central California east to and including the Sierra Nevada and Cascade Mountains " and adds " In most parts of California the presence of beavers is only made known by the stumps of the trees and saplings that they have cut . "
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Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
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