Hebgen Lake starts out just south of here in a fairly open area. It is formed by a dam along the Madison River, and after the dam, the river goes through the Gallatin Canyon.
In 1959, a 7.5 on the Richter scale earthquake caused an enormous landslide that blocked the river downstream, trapping over 200 campers and killing 28 people. (See http://www.fs.usda.gov/detail/gallatin/specialplaces/?cid=stelprdb5127785.) Here you can see how a large chunk of the mountain just slid down.
The river was blocked and formed a new lake between the dam and this landslide. The campers were trapped because the road to get in and out was blocked and water was rising because of the river being blocked. Most were able to get to higher ground, but it took a while for the forest service to rescue them and lead them out on an old unpassable road. Made me think about having to leave my motorhome and all of my belongings in such an emergency.
This graphic shows how the canyon profile was forever changed.
Anyway, this was an interesting place. I stopped at several pull-offs to look at the interpretive signs and take pictures. There is a visitor center but it is closed until May 2014.