All North American "Ceratosaurus" finds come from the Morrison Formation, a sequence of shallow marine and alluvial sedimentary rocks in the western United States, and the most fertile source for dinosaur bones of the continent. According to radiometric dating, the age of the formation ranges between 156.3 million years old (Mya) at its base, and 146.8 million years old at the top, which places it in the late Oxfordian, Kimmeridgian, and early Tithonian stages of the Late Jurassic period. "Ceratosaurus" is known from Kimmeridgian and Tithonian strata of the formation. The Morrison Formation is interpreted as a semiarid environment with distinct wet and dry seasons. The Morrison Basin stretched from New Mexico to Alberta and Saskatchewan, and was formed when the precursors to the Front Range of the Rocky Mountains started pushing up to the west. The deposits from their east-facing drainage basins were carried by streams and rivers and deposited in swampy lowlands, lakes, river channels, and floodplains. This formation is similar in age to the Lourinhã Formation in Portugal and the Tendaguru Formation in Tanzania.