They come down out of the higher elevations as the weather cools in September and October. During the day they hang out in the wooded areas above the valley. Around 5:00 or so, they start to come out in the open to graze. People start to show up about the same time, by the carload and busload, to hang out by the side of the road and watch the elk.
The valley is named for the meandering "horseshoe" bends of the river running through it.
The picture was taken from a turn-out on a road that goes up over the mountains across the continental divide.