Horsetail Fall flows over the eastern edge of El Capitan in Yosemite Valley. This small waterfall usually flows only during winter and is easy to miss. On rare occasions during mid- to late February, it can glow orange when it's backlit by sunset. This unique lighting effect happens only on evenings with a clear sky when the waterfall is flowing. Even some haze or minor cloudiness can greatly diminish or eliminate the effect. Although entirely natural, the phenomenon is reminiscent of the human-caused Firefall that historically occurred from Glacier Point.