I went mountain biking with Bill Nelson along the Minnesota River bottoms this week and he showed me an area just east of Cedar Ave. where beavers have been gnawing away at a dozen or more large trees.
The Wikipedia entry for beaver says:
Beavers fell trees for several reasons. They fell large mature trees, usually in strategic locations, to form the basis of a dam, but European beavers tend to use small diameter (<10 cm) trees for this purpose. Beavers fell small trees, especially young second-growth trees, for food.
But it’s puzzling because the trees above are not in place where the logs could be used to "form the basis of a dam" and they’re much too large for beavers to move.
So Bill and I have a formulated a theory: it’s a training facility. Prove us wrong if you dare.