GUARDIANS
American bison bulls in front of dunes, Great Sand Dunes National Park, Medano Ranch, Colorado. (Bison039)
American bison bulls in front of dunes, Great Sand Dunes National Park, Medano Ranch, Colorado. (Bison039)
Migrating female western phalaropes stopping over at Blanca Wetlands, San Luis Valley, Colorado. (Dunes067)
Flock of sandhill cranes parachuting in for a landing at sunset, San Luis Valley, Colorado. (Crane039)
Prairie sunflowers (Helianthus petiolaris) in Great Sand Dunes NationalPark, San Luis Valley. (Dunes073)
Red aspen after autumn snowstorm in San Luis Valley. (Dunes103)
Rainstorm at sunset, Great Sand Dunes National Park, San Luis Valley. (Dunes058)
Rio Grande below Sangre de Cristo Mountains, The Rio Grande originates at the north end of the San Luis Valley and exits into New Mexico at the south end. (Dunes003)
Prairie sunflowers (Helianthus petiolaris) growing on sand dune at Great Sand Dunes National Park, San Luis Valley. (Dunes081)
Wheeler Geologic Area is formed by erosion of volcanic tuff and ash. San Juan Mountains at the edge of the San Luis Valley. (Dunes025)
Dunes and sunflowers in Great Sand Dunes National Park, San Luis Valley, Colorado. (Dunes020)
Herd of mule deer bucks (Odocoileus hemionus) in prairie sunflowers at Great Sand Dunes National Park, San Luis Valley, Colorado. (Dunes101)
Reflection of full moon over San Luis lake, Great Sand Dunes National Park, San Luis Valley. (Dunes037)
Fall aspen leaves float on top of a calm pool of water. San Luis Valley, Colorado. (Scenic187)
Mule deer (Odocoileus hemionus) tracks filled with narrow-leaf cottonwood leaves in autumn. Great Sand Dunes National Park, San Luis Valley, Colorado. (Dunes042)
Elk (Cervus elaphus) herd on Medano Ranch, Great Sand Dunes National Park, San Luis Valley, Colorado. (MedanoZapata017)
Sunrise over Great Sand Dunes National Park, San Luis Valley. (Dunes012)
Bison herd on frosty morning, Medano Ranch, Great Sand Dunes National Park, San Luis Valley, Colorado. (Dunes106)
Aerial of Cotton Lake. Dry wetland on Medano Ranch, Great Sand Dunes National Park, San Luis Valley. (Dunes092)
Prairie sunflowers (Helianthus petiolaris) and muhly grass (Muhlenbergia filiformis), Great Sand Dunes National Park, San Luis Valley. (Dunes063)
Autumn branches dusted with snow. (Dunes114)
Deadman Creek artesian water, Great Sand Dunes National Park, Medano Ranch, San Luis Valley, Colorado. (Dunes171)
A handful of prairie sunflowers (Helianthus petiolaris) grows into the dunefield. Great Sand Dunes National Park, San Luis Valley. (Dunes016)
Northern pintail ducks and greater sandhill cranes during spring migration. Monte Vista National Wildlife Refuge, San Luis Valley, Colorado. (Birds081)
Aerial view of Great Sand Dunes National Park, San Luis Valley, Colorado. (Dunes036)
Dust storm approaching Great Sand Dunes National Park, San Luis Valley. (Dunes017)
Swirling aspen leaves, San Luis Valley, Colorado. (Dunes009)
Checker mallow wildflower, San Luis Valley, Colorado, Great Sand Dunes National Park. (Dunes061)
Two bison bulls set off the landscape adjacent to Great Sand Dunes National Park. (Bison008)
Broad-tailed hummingbird feeding at rocky mountain bee plant (Cleome serrulata) at Great Sand Dunes National Park in Colorado's San Luis Valley. (Dunes057)
Artesian Big Spring Creek flowing through Great Sand Dunes National Park on the Medano Ranch in the San Luis Valley. (MedanoZapata008)
Blowing sand, Great Sand Dunes National Park, San Luis Valley. (Dunes030)
Snow on fall aspen trees along creek, San Luis Valley. (Dunes113)
Long-billed dowitcher stretching wings, Blanca Wetlands, San Luis Valley, Colorado. (Dunes116)