Mountain Beaver Aplodontia rufus May 13, 1931 S. Lake ridge Tract - B miles S. Seattle City Limits. This locality is in a creek bottom that has been ornamented + retat landscaped. The lower part is heavily overgrown with sweet grass and there were many large runways + burrows the hummocks and small raises in the ground. These burrows average 6-8" in diameter and were evidently in use for fresh tracks were seen in nearby mud. Just how much work a single beaver does was indeterminate as too short length of stay was possible for any specimens procured. The burrows were found in the drier, higher parts of the banks. Down in the cross + grass many Zapus were taken. Incidentally the locality is 14 miles from the shore of the Lake Washington.