I'd like to correct one thing. This is not a "mud slide", it's a true land slide. Mostly rock, gravel and a little dirt, but it seems to be a major movement of earth. I'm in Utah, and we are experiencing slides all over the state, some large like this, some small. One town in Southern Utah has been warned to evacuate after a slide crushed a house and killed two. The state geologists are worried the whole butte could come down.
Remember, Jackson is in a high earthquake active area, and these things can surprise folks where they happen.