Hoar frost (Raureif) in the San Luis Valley, Colorado. The San Luis Valley is the world's largest alpine valley at 8,000 square miles. Much of the valley was covered by Spanish-Mexican Land Grants, including the Luis Maria Baca No.4, generally referred to as the Baca Float No.4. Underlying the valley is a huge aquifer that provides water for agriculture. There has been an effort by a group of Canadian lawyers to buy the land and transfer the water rights attached to the land to the Eastern slope of the Rockies and Denver. If that happens it would bring agricultural activities in the valley to an end. In the distance is the Sangre de Cristo Mountain Range with peaks exceeding 14,000-ft. This picture was taken in November 1986 and later scanned, Sig..