This is a roadside waterfall in upper Yellowstone known as Undine Falls. It is not too far East from Mammoth Hot Springs at the North Entrance
Photo taken October 1st, 2009
Driving along the highway I noticed the sign for the falls and pulled off the highway to a parking lot. I don't recall that you can see the falls from the road, but once at the lookout this view takes your breath away. It was a crisp autumn afternoon, cold enough to keep the snow on the trees that had fallen the night before.