What he found; however, were thousands of them and spent many years digging them up and shipping them to Pittsburgh, where many skeletons are now on display. President Woodrow Wilson heard about the great dinosaur quarry that Douglass had established and proclaimed the site as the Dinosaur National Monument in 1915. Years later, the National Park Service began to develop the quarry as it is today. The rock layer containing the fossil bones forms one wall of the Quarry Visitor Center. On this wall, paleontologists have carefully chipped away the rock to uncover the bones and leave them in place. More than 1,500 fossil bones can now be seen in this unusual exhibit.

The reason why there so many bones at Dinosaur National Monument is that the rock around them is made up of sand and gravel, much like what you might see along a large river. Such a river flowed through this area 150 million of years ago, and the many dinosaurs that lived near it sometimes died near the river. During rainy seasons, the river overflowed its banks and picked up some of the dead dinosaurs lying nearby and their  bodies were carried by the river and deposited in the main channel.

As millions of years passed, the river vanished as other rivers and seas came and went, leaving layer after layer of sand and mud that slowly solidified into rock. Even the buried bones became as hard as rock, as water seeping through the ground filled them in with dissolved minerals. Later still, strong vise-like forces began squeezing the Earth's crust in this area, bending and tilting the rock layers. But the more that the rocks were pushed upward, the more they were worn down by rain, snow, frost, and wind --layer after layer. Finally, some of the long-buried dinosaur bones began to show up near the top of a steep hill, and Earl Douglass found them.

The bones found in the Quarry belonged to eleven kinds of dinosaurs, including allosaurus, stegosaurus, sauropods, ornitholestes, and others. More than half of all the different kinds of dinosaurs that lived in North America in the late Jurassic Period are found in the Dinosaur National Monument Quarry. While the main exhibit wall of dinosaur fossils is closed, some fossils can be seen by hiking ½ mile from the Visitor Center.