Once a year for a period of approximately two weeks, an interesting phenomenon occurs that attracts photographers from around the world. The phenomenon is known as the "natural firefall" and occurs when the setting sun lights Horsetail Fall and turns it a bright orange so that it resembles the old firefall that used to take place at Glacier Point.
For many years, every night of the summer there would be a giant bonfire lit on Glacier Point. People would gather at Curry Village and throughout the east end of the valley to hear the caller shout "Let the firefall begin!" and then the burning embers of the fire would be pushed over the edge of Glacier Point and fall down the cliff toward the valley floor. The National Park service discontinued this activity in 1968. So today, the closest thing is the "natural firefall."
Horsetail Fall takes on the appearance of fire being pushed over the rim of El Capitan as the sun is setting. It takes all the right conditions to make this happen. Sufficient water has to be flowing in Horsetail Fall, the setting sun needs to be at the correct angle, and the sky has to be clear to the west. All these variables take place only the last two weeks in February, with the third week being the most optimal, and hundreds of photographers flock to Yosemite Valley to wait for the light!