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 Ski Valley, which is the southernmost ski destination in the US. The ski area covers the slopes of Mount Lemmon, which reaches an elevation of about 9,100 feet at the summit and can receive around 180 inches of snow annually.