MORRISON DINOSAUR QUARRIES – PAST, PRESENT, LITHOLOGICAL CLUES, AND WHICH QUARRY IS WHICH?

The first Colorado Dinosaur quarries are located on the Dakota Hogback near the Town of Morrison, Colorado. Of the twelve sites where fossils were collected, Quarries 5, 8, and 10 are the sites of most paleontological relevance while Quarry 1 holds mostly historical significance. Quarries 5 and 10 are being reinvestigated, and new discoveries have been made.

Quarry 5, also called the Bone Quarry, is located along the Dakota Hogback and is part of the Dinosaur Ridge Natural National Landmark. The rocks at Quarry 5 are fluvial sandstones containing disarticulated dinosaur bones and dinosaur footprints in the lower sandstone beds. Rip-up clasts, clay drapes, and trough cross-bedding demonstrate the fluvial nature of these sandstones. The dinosaur bones at Quarry 5 are a reddish-brown color, a result of a uranium-bearing mineralizing fluid. Arthur Lakes discovered the genotype of Stegosaurus armatus at Quarry 5 in 1877. Footprints of a juvenile and an infant dinosaur were discovered at Quarry 5 in 2005 by researchers from the Morrison Natural History Museum (MNHM).

Quarry 10 is located above the Town of Morrison along the Dakota Hogback, and was excavated in siltstone overlain by footprint-bearing sandstone. The sandstone caprock has been informally named the Ceiling Sandstone. The bone-bearing layers consist of two one-meter thick layers of dark-grey siltstone, separated by a one-meter thick layer of light-green siltstone. The dinosaur bones in the rocks of Quarry 10 are black or grey in color, as opposed to the reddish-brown bones seen at Quarry 5. The type specimen of Apatosaurus ajax was discovered at Quarry 10 by Arthur Lakes. Researchers from the MNHM discovered the first Colorado stegosaur hind track in the Ceiling Sandstone. Artifacts from Arthur Lakes and his crew have also been recovered. These artifacts include a belt buckle, nails, and beams used to support the Ceiling Sandstone. Dinosaur bone fragments and freshwater clams have been found in the siltstone spoil pile left behind from Lakes’ excavations. The clams are noteworthy because of the lack of freshwater aquatic vertebrates at Quarry 10.