When American military aircraft are retired from active service
(and not sent to a museum), They are stored in the "Bone Yard" near Davis Monthan Air Force Base in Tucson, Arizona. More than 4,000 aircraft are maintained there by the 309th AMARG.
The climate conditions at Davis Monthan, combined with preservation of the aircraft allow many of these aircraft (in theory at least), or scarce parts from them to be returned to active service if necessary.
It is quite a sight to see. Even the precision in the way they are parked is impressive.
It's difficult from pictures alone to comprehend the size of the 'Bone yard' and the number of aircraft stored there. Two of the aircraft in this picture parked side by side or nose to tail would be wider or longer than a football field (>100m).
If you are ever near Tucson, tours are available through the Pima Air Museum, located near the Base.
The museum and the bone yard are popular attractions.
It is difficult to comprehend the number of military aircraft in storage. Even if you have seen these photographs before, it is worth looking again. The 3rd largest Air Force in the world is sitting on the ground here. An "unofficial" AMARC web site provides additional pictures and details on many of the aircraft that have been stored here (AMARC was the former name of the maintenance group). Unfortunately, some of the pictures listed on their site may no longer be available. When aircraft are no longer useful in the inventory they are demolished and sold for scrap.