Diggin' For Dinosaurs - Dinosaur Ridge
The layers of the Jurassic age Morrison Formation have spilled forth a cornucopia of dinosaur bones throughout the western United States. It all started here at Dinosaur Ridge in 1877 when Arthur Lakes, a schoolteacher, made the first major dinosaur bone discoveries in the country. From sandstone that once formed the beds of rivers, Lakes liberated the remains of Stegosaurus, now Colorado's state fossil, and of brontosaurs such as Apatosaurus and Diplodocus, the largest dinosaurs then known.
The remarkable fossils and environmental traces visible along Alameda Parkway are protected as a national natural landmark. A small, free museum with guidebooks and exhibits on local geology and palaeontology sits at the eastern foot of the ridge, near the intersection of the parkway and Colorado Highway 470. You can hike along the road's shoulder to see the fossils at any time (be mindful of the traffic), or you can time a visit to coincide with one of the "Dinosaur Discovery Days" sponsored by Friends of Dinosaur Ridge, when the road is closed to traffic and guides lead tours and answer questions.
Hiking up and over the ridge from west to east, a little over a mile, with a 200 foot change in elevation - is a journey through geologic history. You start in the Jurassic shale and sandstone of the upper Morrison, deposited about 150 million years ago on a coastal plain. Near the western foot of the ridge is a covered area where the fossilized remains of a brontosaur can be viewed. (These bones were left behind after Lakes shut down excavation in 1879.) Ribs, back, and leg bones, as well as less identifiable bits and pieces, protrude from boulders and a thick sandstone layer that once formed a riverbed where the jumbled bones were deposited and buried. Here, you can touch a piece of the past without fear of being chastised by a museum guide.
A little farther on, the purplish siltstone and mudstone of the Morrison give way to the overlying sandstone and shale of the Dakota Group. These rock layers, about 300 feet thick, were deposited starting 135 million years ago, when the shore of a midcontinental ocean called the Western Interior Seaway began advancing west from Kansas across Colorado.
Around 100 million years ago, the shallow sea (at times it was no deeper than 10 feet) stretched from the Arctic Ocean to the Gulf of Mexico. Its western edge eventually reached to where Dinosaur Ridge rises from the plains today, and where the undulating shore once harbored sandy beaches fringed by mangrove swamps.
Just after the road crests the ridge, it turns north and descends the eastern flank. To the left, a slab of yellowish sandstone preserves a series of long, parallel ripples that look as if they were formed just yesterday rather than 100 million years ago. Down the road are more clues to the nature of this ancient environment. Stains on the rock's cream'colored surface resemble rust spots the size of quarters. These may show where mangrove roots once anchored a tree in soft sand. Look closely enough at the rock and you may see impressions of sticks and logs from the former dense, dark tangle of vegetation.
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