Yosemite’s Horsetail Falls prior to becoming a spectacular reddish color in Yosemite National Park on Friday, Feb. 22, 2019. This photo was taken with the SIGMA 60-600mm F4.5-6.3 DG OS HSM Sports lens set at 600mm. This effect only happens around mid February if conditions are right. There has to be enough snow at the top of El Capitan, it has to be just warm enough for some of the snow to begin melting, the sun has to set at just the right angle and there has to be clear western sky so that sunlight illuminates the falls.