Jurassic National Monument near Cleveland, Utah, contains the Cleveland-Lloyd Dinosaur Quarry, the densest known concentration of Jurassic dinosaur fossils. In the Morrison Formation’s Brushy Basin Member, bones accumulated on a floodplain in a seasonal floodpond between river channels. Systematic excavation began in 1927 and later campaigns revealed more than 16,200 disarticulated bones, dominated by carnivorous dinosaurs, especially Allosaurus, with rarer predators and herbivores also present. Scientists have debated whether the assemblage formed in a predator trap or during drought, with no single explanation accepted. Long a major research and museum source, the site became a National Natural Landmark in 1965 and Jurassic National Monument in 2019.