When the setting sun hits Horsetail Fall, it creates an optical illusion that transforms the water coming off the rocks into what looks like molten lava pouring down the granite face of El Capitan.

According to the US National Park Service, the fiery effect appears only in mid to late February, and only on clear evenings when the waterfall is flowing.

Horsetail Fall, in California’s Yosemite National Park, typically runs only during winter, and even slight haze or cloud cover can greatly diminish the display, according to the NPS.