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Dinosaur Ridge EarthCache

A cache by cmclelland Send Message to Owner Message this owner
Hidden : 02/08/2005
1.5 out of 5
1.5 out of 5

Size: Size:   not chosen (not chosen)

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Geocache Description:

PLEASE BEWARE OF TRAFFIC!!! (although I think they may have closed off the road now, but not sure if it is permanent) Located along Alameda Avenue road cut. There are some man-made seats, coverings, rails and descriptive signs. Altitude: 6087' to 6199'. Dinosaur Ridge is part of the Morrison Fossil Beds National Natural Landmark. It is State Law that nothing can be removed from the site.

One may walk, bike or take the shuttle from the visitor's center. The shuttle is $3.00 per person (children under 5 are free) and available from 9am to 4:30pm 7 days a week.

The coordinates given locate a parking area on Alameda Avenue at 'Dinosaur Ridge'. This area is part of the Dakota Hogback, formed from resistant Dakota sandstones of Cretaceous age (135 - 65 million years ago [ma]).

This roadcut exposes outstanding outcrops of the Morrison Formation, a reddish sandstone of Jurassic age (190-135 ma), below the Dakota Group, that contains dinosaur fossils. This extensive formation is found from Arizona to Montana, but this is the type section. The sediments that these rocks are made of came from a large mountain system to the west called the "Ancestral Rockies" that were rapidly eroded and deposited to the east basin as they rose. A shallow sea inundated this area at times as well. Over 109 dinosaur bones are said to be visible near the base of the outcrop here.

Head down the road to N39 40.656 W105 11.645. Here are the Brontosaurus Bulges, sediment filled depressions bulging out of the bottom of a sandstone layer, believed to be the impressions of a large dinosaur's footprints, preserved in soft, sandy mud above sand.

Continue to N39 40.711 W105 11.706. This location is well developed for all to see the jumble of dinosaur bone fossils, all in situ. This famous location is where Arthur Lakes in 1877 first found fossils of Jurassic aged Apatosaurus (=Brontosaurus), Allosaurus, and Stegosaurus. The bones still in place are brown in color and have a spongy pattern. Unusually, the fossils here do actually contain some fragments of the original bone (most fossils are completely replaced by minerals) that are in the 150 million year old range. It is believed these dinosaur bones were washed into a river and immediately buried, allowing them to be preserved and fossilized.

At N39 40.545 W105 11.578 (carefully cross the road before you get to the hairpin curve!) there is a distinct layer of volcanic white ash. This ash is dated at ---(see display at the site and question below) and is compacted tightly to less than 1/12 of its calculated original thickness.

An unusual structure which kids refer to as the 'dinosaur egg' is located near N39 40.541 W105 11.568. Although it may be spherical concretion or nodule weathering out of the sandstone, it is also believed it could be similar to the now eroded feature that left the spherical hole below it, which was formed when an iron-encrusted fossil log eroded (Norm Cygan, Geological Reconnaissance of Dinosaur Ridge and Vicinity, 2002 GSA Annual Meeting, Denver, CO).

Back across the street at N39 40.587 W105 11.531 are the famous ripple marks of the area. Beautiful and varying in size, symmetry, and direction, these indicate that the area was the western shore of the Cretaceous Interior Seaway, an inland sea of the central U.S. The depth of the water varied throughout the time of deposition of these sands. The ripples are in the Dakota Sandstone, and as you head to the next waypoint, keep your eyes peeled for evidence of plant and animal life. There are fossil impressions of worm and crustacean tracks and burrows, of mangrove plants, and of what are believed to be crocodile claws and of rays swimming along the shore. Other small invertebrate trails and tracks are also present. These show that the area was also swampy at times.

The most impressive tracks are further up in the sequence at N39 40.859 W105 11.538. At least five types of dinosaur tracks have been identified. The most common tracks are in this outcrop, and include those from plant eating iguanodontids and the smaller, carnivorous ornithomimid. This outcrop is well marked with labels and signs, so enjoy. Many of the tracks have been darkened with a semi-permanent charcoal by amateurs and by scientists to help distinguish and reveal the tracks. There are other unmarked dinosaur tracks outside of the fenced area, but they are in steep and slippery locations.

There are plans to someday close off this section of the road, build a visitor center, more interpretive exhibits, and more structures for viewing. Until then take care of cars and enjoy the views!

To LOG this site, please submit a picture in front of one of the features and submit answers to the following questions: 1. About how far apart (average) are the Brontosaurs (Apatosaurus) footprints? 2. How old is the white ash layer, according to the explanatory text in front of it? 3. Are the dinosaur bones at stop 2 older or younger than answer 2? (Think about the layers and their position relative to each other).

These notes come mainly from "Geological Reconnaissance of Dinosaur Ridge and Vicinity; 2002 GSA Annual Meeting, Denver CO" Field Trip

Additional Hints (Decrypt)

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Decryption Key


(letter above equals below, and vice versa)

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