One of the best sites in the world for the preservation of these huge beasts is the Morrison Formation of south- western U.S.A. The formation covers a huge area from Montana in the North to New Mexico in the south and Utah in the west. (Top right image courtesy of the Town of Morrison).
The site contains body fossils(many complete) of Sauropods such as Diplodocus, Apatosaurus and Brachiosaurus. Here we see the quality of some of the fossils preserved in the Morrison Formation. (Bottom right image courtesy of Columbia University).