Horsetail Falls, located in Yosemite National Park, is a seasonal waterfall that runs approximtely December through April, depending on snow melt. It falls off 1,000 feet on the east side of El Capitan into Yosemite Valley
During special days in February, when the sun is setting to the west, the sunlight hits the falls making it look like the water is on fire. The water turns orange and sometimes red as if lava is flowing off the mountain. The "firefall" effect generally happens during the second half of February. A clear sky is necessary for the waterfall to glow orange.
This effect can be seen from various locations in the Yosemite Valley. The easiest access to the views are along the roadside turnouts on Northside Drive west of Yosemite Lodge and east of El Capitan.