After a year with heavy snowfall, horsetail falls in Yosemitee National Park will flow. For about one week in February, the sun sets in Yosemite Valley in such a way that the water falling will glow a bright orange and appear as fire. The skies must be clear in order for the sun to illuminate the water. So, if there is snow runoff, no clouds and you happen to be in Yosemitee one of the ten or so days the sun is aligned, you can witness this "firefalls" effect. Be warned, you won't be alone. Thousands of tourists and photographers flock to the spectacle every year and will camp for days to get a pristine composition.