FYI if you are driving extensively throughout the four corners region, there are still some roads on Indian land that are unimproved, or essentially gravel. This is particularly true in the Hopi and Navajo Nations in Arizona, and less so in Colorado.

(The Federal government has failed to maintain or adequately develop the roads in these areas of their responsibility for the past four decades or so, and except in southern Colorado, where local government has stepped up, the local populations continue to suffer this active neglect today.)

Some of the AAA maps will indicate the distinction with an orange or yellow overlay of the parts of the roads that unimproved, but this isn't always obvious at first glance. Google Maps will often call this fact out in marginal notes. It can happen that you are cruising along and suddenly the surface will change for miles. Just slow down and take it easy, as often the alternate route would include hours of back-tracking.