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