Quaking aspen trees (Populus tremuloides), with their golden-yellow fall foliage, are perhaps the dominant fall foliage tree of western North America. It is from this fall foliage standout that the ski resort of Aspen, Colorado derives its name. In the Rocky Mountains there are stands of quaking aspen trees that stretch for miles, their autumn gold perhaps punctuated here and there by an evergreen or two, as if for contrast. Quaking aspens are closely related to poplar trees, such as Lombardy poplar trees.