Fossil log and dinosaur bones in the Jurassic of Utah, USA.

This is a sandstone exposure of the Morrison Formation, an Upper Jurassic unit that is widely distributed in many western American states. The Morrison consists of fluvial (river/floodplain) and lacustrine (lake) deposits, plus reddish-colored paleosol horizons. Dinosaur bones and dinosaur tracks are moderately common in Morrison Formation sediments. Exceptionally rich localities include Como Bluff in Wyoming, Dinosaur National Monument in Utah (= this site), Dinosaur Ridge in Colorado, and the Cleveland-Lloyd Quarry in Utah.

The dark-colored, elongated object in the middle of the picture is a fossil log. The surrounding fossils are dinosaur bones from various species. This richly fossiliferous bed is a fluvial sandstone, pebbly sandstone, and conglomerate (many of the pebbles are angular to subangular, however). Disarticulated and partly-articulated dinosaur bones are abundant, as are bivalves (clams). The unit is traditionally interpreted as a flash flood deposit in an ancient river environment. The sandstone and bones are also interpreted as having been deposited near a breached levee during a flooding event on a floodplain. Such deposits are called crevasse splays.

Stratigraphy: Carnegie Quarry Sandstone, Brushy Basin Member, Morrison Formation, Kimmeridgian Stage, Upper Jurassic, ~150 to 156 Ma

Locality: Carnegie Quarry, Dinosaur National Monument, northern Uintah County, northeastern Utah, USA

See info. at: <a href="https://en.wikipedia.org/wiki/Dinosaur_National_Monument" rel="noreferrer nofollow">en.wikipedia.org/wiki/Dinosaur_National_Monument</a> and