Alamosaurus sanjuanensis was originally described from a left scapula (USNM 10846) and right ischium (USNM 10847) discovered in the Late Cretaceous Ojo Alamo Formation of New Mexico in 1921 (USNM quarry 15560). In 1937 a second specimen was found in the North Horn Formation of Utah, consisting of a partial skeleton (USNM 15560), comprised of a mostly complete pelvis and caudal vertebral series, from the Late Cretaceous. A sacral complex with five vertebrae was observed in the field but was not collected. In 1966 James “Jim” Jensen of the Brigham Young University Earth Science Museum relocated the Gilmore quarry and found the sacrum, which, by then, had “rotted down into brown soil” and could not be recovered. Nearby, Jensen discovered the proximal heads of a humerus and femur and an isolated proximal caudal vertebra, none of which belonged to USNM 15560. Mike Morales and a team from the University of California at Berkeley discovered additional caudal vertebrae in the vicinity also, none of which belonged to the specimen collected by Gilmore. The specimens recovered by Jensen and Morales are significant because they indicate the presence of additional Alamosaurus specimens in the North Horn Formation. Additionally, the humerus is the most complete Alamosaurus humeral head yet discovered.