The terrestrial sediments of the Morrison Formation-eroded from rising highlands to the west-were deposited on top of the marine Sundance sediments as the sea regressed for the last time late in the Jurassic .
The terrestrial sediments of the Morrison Formation - eroded from rising highlands to the west - were deposited on top of the calcareous Sundance Formation as the sea retreated for the last time , late in the Jurassic .