Some more northerly examples are the Crazy Mountains, Castle Mountains, Bears Paw Mountains, Highwood Mountains, and Little Rocky Mountains, all in the US state of Montana. Each of these ranges is forested and has tundra and snowpack above treeline, but is not connected to any other range by forested ridges; the ranges are completely surrounded by treeless prairie and/or semi-arid scrubland below. Other well-known sky islands of North America are the Great Basin montane forests, such as the White Mountains in California, and the Spring Mountains near Las Vegas, Nevada. One of the unique aspects of the sky islands of the U.S.-Mexico border region is the mix of floristic affinities, that is, the trees and plants of higher elevations are more characteristic of northern latitudes, while the flora of the lower elevations has ties to the desert and the mountains further south. Some unique plants and animals are found in these sky islands, such as the mountain yucca, Mount Graham red squirrel, Huachuca springsnail, and Jemez Mountains salamander.