(Click for high res version.)
It also wonderfully illustrates the reason the lake's there - the Slumgullion Slide dammed the river. Here's a great resource for those interested in learning more about the slide. The landslide episode that created the dam occurred about 700 years ago.
A section of the slide is still active. Here's another rendering showing the active portion in red, with the inactive portions in blue.
(Click for high res version.)
And here's an animation showing patented mining claims in the Alpine Loop area:
