This is the Dinosaur Quarry at Dinosaur National Monument in both Utah and Colorado (The Quarry is actually in the Utah portion of the National Monument). The Quarry is now covered by the Quarry Exhibit Hall. Here is a quote from the
National Park Service, Dinosaur National Monument website:
The Quarry Exhibit Hall allows visitors to view the wall of approximately 1,500 dinosaur bones in a refurbished, comfortable space. Here, you can gaze upon the remains of numerous different species of dinosaurs including Allosaurus, Apatosaurus, Camarasaurus, Diplodocus, and Stegosaurus along with several others. Exhibits, including an 80-foot long mural, reveal the story of these animals and many others that lived in the Morrison environment during the Late Jurassic. There are even several places where you can touch real 149 million-year-old dinosaur fossils!
Rangers are available to answer questions and occasionally give Junior Ranger programs or talks on different topics related to the quarry or dinosaurs throughout the day during the summer.
Excavation started back in 1909 and ended in 1990. See "The Real Story Behind the Dinosaur Quarry" for more information.