May 17
Every February, Horsetail Fall on El Capitan turns into what looks like flowing lava. The setting sun hitting the waterfall at a precise angle for a few minutes before sunset, turning the water bright fiery orange.
It is a rare event, like a solar eclipse, and is considered a once in a lifetime opportunity to experience.
Three things have to align at once for it to happen. The sun's path only lines up with that cliff face during a narrow window in mid to late February. The fall needs enough snowmelt to actually be flowing, and the sky has to be completely clear for the low angle light to hit with full intensity.
