The Aerospace Maintenance and Regeneration Group (AMARG) aka "The Boneyard" is located at Davis-Monthan AFB in Tucson, AZ. The Boneyard is an open-air, desert storage facility for retired military aircraft. Many of these aircraft are in a state of preservation and, therefore, available to be called back to service if needed. Certain airframes, such as the B-1 Lancer and A-10 Thunderbolt II, are being picked over for spare parts to support aircraft on active duty. Airframes that are completely useless are likely awaiting their demise at the nearby smelter. There are numerous F-4 Phantoms and F-16 Fighting Falcons at the Boneyard and many are being converted to QF-4 and QF-16 target drones.
(Photo: AMARG Public Affairs Office)
All of the great, cold-war era bomber fleets have passed through the Boneyard. The B-36 Peacemaker, B-47 Stratojet and B-58 Hustler strategic bombers largely met their downfall at the Davis-Monthan smelter. Many of those aircraft that escaped the smelter are on display at various museums and airparks around the country. The nearby Pima Air & Space Museum has a very nice collection of such aircraft.
Thanks to Toiyabe from arfcom for help in IDing some of these aircraft.
Public bus tours are available via the Pima Air & Space Museum but, unfortunately, you are not allowed to leave the bus during the tour. An interesting alternative would be to rent an airplane and make a few passes over the storage areas. That's just what author Nick Veronico did and you can see the photos in his excellent book, AMARG: America's Military Aircraft Boneyard.