William Henry Jackson becomes the first person to photograph Colorado’s elusive Mount of the Holy Cross, providing reliable proof of its existence.

Rumors had abounded for years that a natural cross of snow lay hidden high in the rugged mountains of Colorado. Many claimed to have seen the cross, but others were unable to find it. In August 1873, the photographer William Henry Jackson set out to prove its existence by taking a picture of it. Jackson was an experienced wilderness photographer who had accompanied wagon trains to California in 1866 and was employed as expedition photographer on Ferdinand Hayden’s survey of the Yellowstone region in 1871. Published in popular mass-circulation magazines like Harper’s Weekly, his images became immensely popular and showed Americans a rugged western wilderness that most would never see firsthand.

Jackson had heard rumors of the extraordinary cross of snow that occasionally appeared on the face of a high mountain peak. Jackson led a small party to the supposed site in north central Colorado in the summer of 1873. Jackson found the cross, though there was nothing miraculous about its cause. After thousands of years of erosion, two deep ravines had formed in the steep rocky face of a mountain peak. Intersecting at a 90-degree angle, the ravines sheltered the winter snow from the sun well after the rest of the mountain snow had melted away. For a brief time, a nearly perfect cross of snow appeared on the rock face, though it often melted away later in the summer.

In the pre-dawn hours of this day in 1873, Jackson prepared the heavy camera equipment he had carried up the mountain opposite the cross. He took his photos of the cross just as the first rays of the sun angled low across the crevassed face, emphasizing the lines of the cross. The best of the resulting photos became one of Jackson’s most popular and famous images, and it ended any further doubts about the existence of the Mount of the Holy Cross.