File:Arthur Lakes' Quarry 10 (Dakota Hogback, Morrison, Colorado, USA) 1.jpg

English: This is the remnants of Arthur Lakes' "Quarry 10", a dinosaur locality on the slopes of the Dakota Hogback next to the town of Morrison, Colorado. The Dakota Hogback's bedrock consists of eastward-dipping sedimentary rocks of Mesozoic age. The beds were tilted during the Laramie Orogeny in the late Mesozoic to early Cenozoic, when the Rocky Mountains uplifted. At Quarry 10, nonmarine shales of the Upper Jurassic Morrison Formation are present. The original excavation was about 40 feet wide and 40 feet deep. Lakes used timbers for support, to prevent the overlying sandstone from collapsing into the quarry. An original timber support is still present at the site, now coated with a plaster field jacket (= white object in front of the geologist in the picture). Collapse events did occur here, but they did not cause any deaths - just broken bones. Yale University told Lakes to close the quarry in 1879. The excavation was filled in using shovels (although Lakes said he blew it up) - the quarry fill is stratified.

Quarry 10 fossils include the type specimen (= the original skeleton) of Apatosaurus, a famous Jurassic sauropod dinosaur. The type Apatosaurus bones were in a very dark gray, organic-rich mudstone matrix - a small paludal environment. The bed pinches out laterally. The skeleton has Allosaurus chew marks on it. Shed teeth from Allosaurus were found associated with the Apatosaurus skeleton. The Apatosaurus died here, possibly from thirst - the site was a foul water hole.

Quarry stratigraphy:

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Black streak ~1 meter thick, with Apatosaurus ajax bones

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Greenish-gray shale, with no fossils

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Gray shale, bearing the type specimen of Apatosaurus ajax

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Large sauropod vertebrae are still in the sandstone unit above the quarry. Lakes observed them, but did not collect them. They are no longer exposed at the surface.

Other Quarry 10 fossils include coprolites that are possibly Allosaurus scat - they have sphincter striations and bolus structures. Invertebrate fossils are also present in the Morrison shales here, including unionid bivalves. Fish fragments have been found in the quarry's spoils pile.

The spoils pile from the original quarry has been processed for fossils in modern times by the nearby Morrison Museum of Natural History.

The shale would easily fall off from the dinosaur bones that Lakes collected, because the matrix was friable mudstone - no preparation was needed. The matrix sloughed off easily when urinated on, because the shale included smectite clay ("swelling clay") - this was done during the original excavation. Bones were sent downslope in chutes and then sent to Yale University.

Stratigraphy: Morrison Formation, Upper Jurassic

Locality: western side of the Dakota Hogback next to the town of Morrison, north-central Colorado, USA