图森附近索诺兰沙漠中的巨柱仙人掌，亚利桑那州 Saguaro cacti in the Sonoran Desert near Tucson, Arizona (© Jack Dykinga/Minden Pictures)

图森附近索诺兰沙漠中的巨柱仙人掌，亚利桑那州 Saguaro cacti in the Sonoran Desert near Tucson, Arizona (© Jack Dykinga/Minden Pictures)

Sky island views

Though it's December, it isn't cold and snowy everywhere in North America. Here, near Tucson, Arizona, the Sonoran Desert stays warm year-round. In this photo, we're looking at a 'sky island'—an isolated, high-elevation woodland surrounded by radically different lowland environments. In this case, the desert land at the base of the mountain is peppered with saguaros—a stately cactus recognized for its long arms. The snow-capped Santa Catalina Mountains in the distance are part of the Madrean Sky Islands and are home to Mount Lemmon Sky Valley, which is the southernmost ski destination in the US. The ski area covers the slopes of Mount Lemmon, which reaches 9,150 feet at the summit and gets about 180 inches of snow annually.