Morrison Formation
According to radiometric dating, the Morrison Formation dates from 156.3 ± 2 million years old at its base, to 146.8 ± 1 million years old at the top, which places it in the later Jurassic. This is similar in age to the Solnhofen Limestone Formation in Germany and the Tendaguru Formation in Tanzania. Throughout the western USA, it lays over the Middle Jurassic Summerville, Sundance, Bell Ranch, Wanakah, and Stump Formations.