Extreme diversity distinguishes the southwest from other U.S. Regions. I-40 (old Route 66) splits the Southwest into two distinct environments: the northern divide has cool climates, tall pines and mountainous terrain, for example, in Santa Fe and Flagstaff. The southern divide is hot, flat and arid, like Albuquerque and Phoenix. A short one hour drive from Albuquerque to Santa Fe provides an unmistakable illustration of the difference in environment.