February is the only month and that for only a few days, that the setting sun narrows its beam to only expose the falls off El Capitan.
Conditions must be perfect. There can be no clouds to diffuse the sunset. There must be water in the fall. You have to be there, duh.
In this particular shot the sun was finally diffused by distant low level clouds, so the intensity did not produce the vivid red and orange coloring, only orange. And, with such minimal snowfall there was little water. But, still pretty. "Horsetail Fall"