Here are some excerpts from an article about Mountain Beavers. The whole article is linked to in the Windmill Oldgrowth sidecolumn.
[Lewis and Clark made note of an animal which the Lower Columbia people favoured "in forming their robes, which they dress with the fur on them and attach together with sinews of the Elk or deer," and which they called the "siwelel." It has gone by many names: Ground bear, whistler, mountain boomer, kickwilly, showtl, ogwoolal, oukala, kula possum, giant mole, ground beaver, and kulata.
Its scientific name is Aplodonta rufa. While the first hint of its existence was whispered to western science in the 1806 journals of Meriwether Lewis and William Clark, scientists have shed little light on its habits. The academic literature remains informed as much by folklore as by clinical, methodical observation. In the standard reference texts, the animal is said to weep great tears when distressed, grind its teeth when angry, and, by some unknown means, utter loud booming sounds.
In his Yellowstone diaries, the great American naturalist John Muir wrote that mountain beavers routinely alter the flow of streams and construct canals to feed intricate subterranean watercourses and to keep the shrubs it likes well-irrigated. "It is startling," he wrote, "when one is camped on the edge of a sloping meadow near the homes of these industrious mountaineers, to be awakened in the still night by the sound of water rushing and gurgling under one's head in a newly formed canal."
Gyug reckons that the creature merely harvests large amounts of nettles, salal and sword ferns and leaves them in piles around its burrows so that they're handy. That's how you find them. Chances are you'll never see a mountain beaver, but chances are good that if you look for one in the right places - rainforest valleys, thick with undergrowth - you;ll find big piles of succulent shrubs, and the ground will be pockmarked with holes.]
The following is from a very good Mountain Beaver site- http://dirttime.ws/Notebook/Aplodontia.htm
[The mountain beaver (Aplodontia rufa) is an interesting but little known mammal unique to the Pacific Northwest. Its range falls mostly to the west of the Cascades, from northern California to southern British Columbia. First described by Lewis and Clark, the mountain beaver remains rather obscure, even here in the heart of its range. It is primarily nocturnal and is seldom seen.
If you have read anything about this fellow, you know that it is neither a true beaver nor strictly a mountain inhabitant. It is a rodent, though. In fact, with a lineage traced back 40 million years, the mountain beaver is our oldest rodent. While this suggests that it has been a very successful species, it also means that the mountain beaver has a primitive physiology. For example, it cannot pant or sweat and has a low reproductive rate. Studies have shown that its kidneys cannot concentrate uric acid as well as modern mammals so it must take in about 20% of its body weight in water daily in order to remove body wastes.]
This link goes to the Citizens for Alternatives to Toxics letter about Windmill dated March 5, 2005. http://www.alternatives2toxics.org/pdfs/SPI_THP3-05.pdf
This one is a another website about Mountain Beavers. http://www.infowright.com/mtbeaver/
This is a photo series of a bold Mountain Beaver in someones garden.http://www.infowright.com/mtbeaver/mtbeavergarden.html
"The largest known variety of flea is (Hystrichopsylla scheffleri). This species of flea is known from only one specimen taken from the nest of a mountain beaver. It was 1/3 of an inch long!"- http://www.oddrob.com/bugfacts.asp
Mountain Beavers are one of the oldest species of flea bitten varmints still in existence. This link from Flea News might take a while to connect on slower computers. Its pretty technical and dry.http://www.infowright.com/mtbeaver/fleamtbeaver.pdf