The U.S. Bureau of Land Management announced the find Monday, calling the quarry near Hanksville "a major dinosaur fossil discovery."
An excavation revealed at least four sauropods, which are long-necked, long-tailed plant-eating dinosaurs, and two carnivorous ones, according to the bureau. It may have also uncovered an herbivorous stegosaurus.
Animal burrows and petrified tree trunks 6 feet in diameter were found nearby. The site doesn't contain any new species but offers scientists the chance to learn more about the ecology of that time, said Scott Foss, a BLM paleontologist.
The fossilized dinosaurs are from the same late Jurassic period as those at Dinosaur National Monument, which straddles the Utah-Colorado state line, and the Cleveland-Lloyd quarry near Price.
It could be a decade or so before the full importance of the Hanksville quarry is known, Foss said. "It does have the potential to match the other major quarries in Utah," he said.
The site, roughly 50 yards wide by 200 yards long, was excavated by a team from the Burpee Museum of Natural History in Rockford, Illinois. Museum officials visited the site for about a week last summer and returned this year for a three-week excavation.
The area has long been known to locals and BLM officials as a dinosaur haven. But no one knew of the site's magnitude until excavation began.
The bones were found in a sandstone channel of an ancient river.
"The preservation of these dinosaurs is excellent," Foss said.
The mix of dinosaurs, trees and other species in the area may help scientists piece together what life was like 145 million years to 150 million years ago, including details about the ancient climate, Foss said.
BLM plans to close the site to conduct an environmental assessment for continued work in the area. The agency isn't disclosing the exact location of the find because of security concerns.