Carol Walker / Two wild stallions standing nose to nose, the older pinto on the left is the band stallion, McCullough peaks, Wyoming, USA. July.

Carol Walker / Two wild horses, sibling fillies, nuzzling, Lost Creek, Wyoming, USA. June.

Carol Walker / Pinto stallion, portrait, McCullough Peaks, Wyoming, USA. October.

Carol Walker / A wild grey pinto stallion trotting over grassland, Green Mountain, Wyoming, USA. May.

Carol Walker / A wild pinto mare with her blanket appaloosa yearling and buckskin filly, walking over grassland, Lost Creek, Wyoming, USA. August.

Carol Walker / A wild black curly stallion bowing his head, posturing at another stallion, Salt Wells Creek, Wyoming, USA. May.

Carol Walker / Two wild stallions fighting, a bay roan and a black stallion, Salt Wells Creek, Wyoming, USA. June.

Carol Walker / A wild red roan stallion rearing up as another stallion approaches, Salt Wells Creek, Wyoming, USA. May.

Carol Walker / Three wild stallions, two greys and a sorrel, standing in a group, Lost Creek, Wyoming, USA. July.

Carol Walker / Wild curly stallion posturing, portrait, Salt Wells Creek, Wyoming, USA. June.

Carol Walker / Wild Bay stallion leading his grey mare across grassland, Lost Creek, Wyoming, USA. July.

Alex Mustard / A diver swimming through the Silfra fissure, a crack in the Earth's crust between the North American and Eurasian continental plates, which is filled with glacial melt water. In this photo the Am...