05/13/2026
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If you’ve ever stood in front of the Wall of Bones inside the Quarry Exhibit Hall and wondered “How do scientists figure all of this out?” — you’re not alone! Fortunately, the answers are written in the rock between the bones!
More than 1,500 dinosaur bones are preserved exactly where paleontologists first uncovered them, still embedded in the sandstone of the Morrison Formation — a rock layer dating back about 150 million years to the late Jurassic period. By studying this layer, scientists realized that this area was once a lush world of rivers, floodplains, and wetlands. Read on for examples of how to read the rocks!
The arrangement of the river channels, along with the way dinosaur bones and sediments are positioned in the rock, shows us the direction the ancient river was flowing. As with rivers today, ancient rivers moved objects in predictable ways based on water flow and how the current interacted with each object. For example, if a large, broken, or jointed log were carried by the river, the heavier end would drag to a stop first as the current slowed, while the lighter end would continue to be pulled downstream by the current. We see a similar pattern in the Quarry Wall, where articulated legs and vertebral columns (bendy and jointed pieces) are preserved.
Similarly, when a single solid piece of debris moves downstream, it tends to “log roll” along the riverbed as the current slows. As it settles, its long axis typically comes to rest at a right angle to the direction of flow.
When dinosaurs died in a serious drought, their carcasses lay in the dry riverbed, rotting apart and being torn apart by large and small scavengers. Eventually, the massive Jurassic rainstorms returned and filled the river. Those flood waters carried the chunks of rotted carcasses downstream and buried them in sand and mud. Over millions of years, those sediments hardened into rock, creating the fossil-rich layer we see today.
Geologists read the surrounding rock layers like pages in Earth’s diary, too. Ripple marks, ancient shorelines, and even the types of sediment tell the story of changing environments — from shallow seas to sandy deserts — long before dinosaurs ever wandered here.
Today, the Quarry Exhibit Hall stands right over the hillside where these fossils were found. It gives us a rare chance to see the bones in place, exactly as the ancient river left them. Every groove, grain, and fossil helps scientists piece together the world of the Late Jurassic — and helps all of us step back in time.
Come read the stories in the rocks for yourself! Nerdy park rangers are here to help translate Earth's stories.
NPS image/ part of the Wall of Bones, showing scattered pieces of dinosaur carcasses exposed in the rock wall
