For just two weeks at the end of February, hundreds of people gather at Yosemite National Park for something very special.
With just the right conditions, the Horsetail Fall down El Capitan glows orange like molten fire.
This natural phenomenon was first stumbled upon in 1973.
There are a few things that need to come together at exactly the right time for it to happen.
At the end of February, the Sun is in exactly the right position in the sky so that five to 15 minutes before sunset, the Sun’s rays pass directly through the waterfall.
Clear skies are needed for a good sunset and there needs to be enough water flowing down the side of El Capitan.
Good snow is needed through the winter so that once the late February sunshine has some strength, it will start to melt the snow.
With enough snowmelt, water runs over the edge of the fall.
The best views of the Yosemite firefall are possible when there is a lot of water so that the glowing stream is more pronounced.
However, even with a trickle, the area of mountain where the water falls will still glow orange.