The Dinosaur Quarry within the Visitor Center building is no longer actively being excavated. The fossil-bearing seam within the quarry building had basically been "played out" by 1991. In the time span since the discovery almost 2000 bones had been carefully extracted. Many others were left where they naturally occur attached to the ancient river channel sediments in which the remains of perhaps hundreds of dinosaurs accumulated and were buried. The fossils left in their original setting often provide information that might otherwise be lost by their removal. Visitors who visit the Dinosaur Quarry can see bones, such as these from an Apatosaurus (once known as Brontosaurus) attached to the original fossil bone bed (NPS, 2000).