Dinosaur National Monument
|Cliffs at Dinosaur National Monument (courtesy, National Park Service)|
Not until about the midpoint of dinosaur history, approximately 145 million years ago, did a suitable habitat develop here—a low-lying plain crossed by several large rivers and many intermittent streams, clad in a variety of ferns, cycads, clubmosses, and clumps of tall conifers. This was home to dinosaurs such as Apatosaurus (better known as Brontosaurus), Diplodocus, Stegosaurus, and other vegetarians, and to the sharp-toothed carnivores—Allosaurus was the largest at this time that preyed upon them. As these animals lived and died, most of their skeletons decayed without a trace, but in at least one spot, river floodwaters washed a great number of carcasses and bones onto a sandbar.
There, mixed with the remains of turtles, crocodiles, and clams that lived in the river, the bones were preserved in the sand. This layer itself was not very thick, but thousands more meters of sediments piled up on top of it as the sea crept in and out during the last part of dinosaur times. Dissolved silica percolating through the strata turned the ancient riverbed into hard sandstone and mineralized the bones buried within it.
When the Rocky Mountains began to rise to the east, this area went along for the ride. Here, the mountain-building did not push up the rock layers from below, but instead it squeezed them from the sides, warping and tilting them, sometimes cracking and shifting them along fault lines. Rain, frost, wind, and gravity slowly but steadily wore away layer after layer of the uppermost strata, revealing the older rocks beneath. In this way, a bit of the long-buried riverbed and its fossil treasure began to show up on the top of a jagged ridge.
Erosion has stripped away the "younger rocks" from most of the canyon country, accentuating the contrast, in both time and environments, between past and present. Land that was once a sea floor where coral and shellfish thrived is now far away from moist ocean winds, and a semi-desert climate prevails. The temperature can vary by nearly 85 degrees C (155 degrees F) between January and July, and though snow cloaks the ground in winter, it contains little water. Rain, when it comes, is often in the form of brief, localized thundershowers, drenching the ground in one place and filling the gullies with flash floods, while dust devils rise in the hot breeze nearby. In this setting, life must be tolerant of extremes. Good looks, as humans rate them, are not very important in the desert. Most of the dry basin and plateau land of the park is covered with sagebrush, greasewood, and saltbush, graduating into "pygmy forests" of pinyon pine and juniper at the higher elevations. Drab as these plants may seem to our eyes, they are beautifully adapted for their special tasks: conserving water, resisting extreme temperatures, and eking out a living from poor soils.
Details mentioned in this article were accurate at the time of publication