In 1909, the Carnegie Museum of Natural History paleontologist Earl Douglass discovered a rich fossil site in Utah, which became protected as part of Dinosaur National Monument in 1915. Excacations at the site lead to the discovery of much additional C. lentus material. A nearly complete specimen of a juvenile C. lentus, CM 11338, was also found at the site by Douglass in 1909, and described by Charles W. Gilmore in 1925. It is the most complete sauropod fossil ever discovered, and nearly every element was in articulation. Later in 1918, the Carnegie Museum collected another complete and articulated skeleton of an adult (USNM V 13786) of C. lentus that was later transferred to the National Museum of Natural History in 1934. The skeleton is now mounted in the NMNH fossil hall. In 1919, the Carnegie Museum's director William Jacob Holland named a new species, Uintasaurus douglassi, on the basis of several cervical vertebrae from the quarry; this species was synonymized with C. lentus in 1958. In 1950, another specimen consisting of an anterior dorsal vertebra from Dinosaur National Monument was named as a new species, Camarasaurus annae; this too is now regarded as synonymous with C. lentus.
