Wild Mustangs, South Dakota, 2004Photograph by Maggie SteberIn the wind-tossed plains of Lantry, South Dakota, two wild mustangs playfully kick and cavort. Descended from Spanish horses brought in by Spanish conquistadors in the 16th century, mustangs represent a tenuous link to America's frontier past. Researchers estimate the U.S. was once home to more than two million mustangs; today there are fewer than 50,000.