Aaron Meyers Photography has some great info on the Fire Falls sunset illusion at Horsetail Fall Yosemite.
Each year thousands of photographers visit Yosemite National Park in hopes of seeing the famous ”Fire Falls” event at Horsetail Falls. Horsetail Falls is a seasonal waterfall that only flows after rain or as the snow melts above El Capitan. It’s located on the west side of El Capitan and can be viewed from a number of locations.
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From the National Park Service:
Photographers flock to Yosemite year round, but there is a special reason they were here this week. There is a small, ephemeral water fall that puts on quite a show in mid- to late-February. Horsetail Fall, on the east shoulder of El Capitan, is a great example of the amazing natural phenomena that exist in Yosemite. A perfect combination of water, rock, and light, the fall glows bright orange at sunset when the conditions are right. Those conditions occur for only a small window when the angle of the sun is right, there is enough water in the fall, and we have clear skies at sunset. Some years the phenomenon only happens on one or two days! Unfortunately, climate change is likely to make this special sight even rarer. Warmer temperatures will reduce the amount of snow that is collected in the very small watershed that feeds Horsetail Fall. This means less water to light up the hearts and camera lenses of viewers here in Yosemite Valley.