"Twisted Rock under a summer sky." by NPS/Michael Thomas , public domain
DinosaurFossil Discovery Trail |
National Park Service
U.S. Department of the Interior
Dinosaur National Monument
Fossil Discovery Trail
The Fossil Discovery Trail winds through numerous titled rock layers
Travel through millions of years of history on the Fossil Discovery
Trail. Long ago, dynamic forces pushed and tilted these layers of rock
upward. Later, erosion exposed the layers as colorful ridges. Erosion
also revealed remnants of ancient ecosystems including now-extinct
animals that inhabited landscapes quite different from what we see
today. Discover more about several of these ancient ecosystems.
Getting Started
Trail Trivia
Length: 1.5 mi/2 km one-way
Elevation change: 150 ft/46 m
Time to hike: about 1 hour
Rock layers exposed:
Stump Formation
Morrison Formation
Cedar Mountain Formation
Dakota Sandstone
Mowry Shale
Frontier Sandstone
Mancos Shale
Geologic time exposed:
Jurassic to Cretaceous
This guide describes the trail as hiked
downhill from the Quarry Exhibit Hall to the
visitor center. Follow the guardrail down the
right side of the road from the exhibit hall
parking lot to find the trailhead. (You may
also hike uphill from the trailhead located
behind the visitor center.) Restrooms and
drinking fountains are available during
business hours near both trailheads.
Restricted Access Road
SHUTTLES ONLY (in Summer)
RANGER-GUIDED (Fall - Spring)
Prepare for this rocky, sun-exposed trail by
wearing good hiking shoes and dress for the
weather. In summer, that means bringing
plenty of water, sunscreen, and a sun hat.
The trail is very slippery when wet.
Please stay on the established trail and leave
all plants, rocks and fossils in place for the
next hikers to discover.
Quarry Exhibit Hall
Dinosaur fossils
Check with a ranger at the
visitor center for more information
Stump Formation
Clam fossils
Morrison Formation
Dinosaur fossils
Quarry Visitor Center
P
To 40 and
Jensen, Utah
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Mowry Formation
Fish scales
ad
Open To All Vehicles
Authorized Vehicles Only
Jo
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North
Fossil Discovery Trail
Split Mountain Anticline
The same tectonic forces
responsible for the uplift
of the Uinta and Rocky
Mountains caused rocks in
this area to wrinkle like a
rug pushed across a hard
wood floor. The trail travels
through the edge of an arch,
or anticline, where layers are
tilted steeply to the south.
On the other side of Split
Mountain, the same layers
tilt to the north.
As you begin your hike, take a moment to
look at the rock layers that are dramatically
uplifted and tilted around you. These were
once horizontal layers of sediment that
eventually turned into flat-lying sedimentary
rock. So how did they end up tilted?
80 million years ago
60 million years ago
About 60 million years ago, rocks here were
pushed up like an arch. Since then, erosion
exposed stronger sandstone and limestone
as ridges while shale formed softer mounds.
Thanks to the tilt, more rock layers are
exposed in a shorter, less steep hike.
30 million years ago
3 million years ago
Morrison Formation
How Old?
One of the more accurate
ways to determine the age of
a geologic layer is to examine
the ratio of potassium to
argon gasses trapped in
crystals of volcanic ash.
Unstable potassium turns
into argon at a stable rate.
By looking at crystals in ash
that contain both potassium
and argon, the ratio of
the two elements gives
geologists an estimate of the
age of a rock layer.
Each step leads you through rock layers
with different colors, textures, and fossils.
Sometimes these differences are subtle,
sometimes striking. Most of the Morrison
Formation is mudstone and clay, but watch
for the trail spur that hugs a sandstone cliff.
This part of the Morrison Formation is made
up of river-deposited sand and gravel. Based
on potassium-argon dating of volcanic ash, in
older and younger layers on either side of the
sandstone wall, this layer is estimated to be
about 149 million years old. Fossil fragments
of dinosaurs are embedded in the cliff along
with impressions of freshwater clams.
The Morrison Formation trail spur follows
the same sandstone layer that is exposed in
the Quarry Exhibit Hall. However, this cliff
has not been worked on by paleontologists
to make the bones easier to see. The first
fossils along the spur are fragments that are
somewhat shiny and dark orange in color.
Some have a spongy-looking interior which
contained bone marrow. Their texture is
generally smooth and their size ranges from
½ inch to 10 inches in diameter.
Find the fossil vertebrae
about 10 feet above the trail.
As you hike along the cliff, the quality and
size of the fossil bones increase. Just past the
mid-point of the spur, the trail dips a few
feet. After the dip, look up on the cliff face
to see eight vertebrae. Keep hiking and look
around waist level for the end of a humerus.
Saving the best for last, a large femur rests at
the end of the spur. Sharp eyes can find more
bones, depending on the angle of the sun.
Mowry Shale
Which is the Mowry Shale?
Look for the grayish mound
of Mowry Shale between
the prominent ridges of
the Dakota and Frontier
sandstones. The older Dakota
Sandstone is a real attentiongetter with 100 million
year old beach sand stained
bright orange and yellow
by minerals. The younger
Frontier Sandstone, formed
from 90 million year old
beach sediments, also proved
to be a good canvas for 1000
year old Fremont rock art.
The Mowry Shale is easy to overlook today,
despite its fascinating history. Along the
coast of an ancient sea, erupting volcanoes
(near the present California/Nevada border)
spewed ash which fell into the salty waters
that covered this area. By studying minerals
decaying in the shale, geologists determined
that the ash was deposited between 93 and
98 million years ago. The ash likely killed
most fish swimming here. Currents at the
bottom of the sea then scattered the scales.
Look for tiny, shiny gray-to-golden fish scales
fossilized in these rocks. Taking the time to
discover even the tiniest of fossils can bring
ancient ecosystems alive in our imaginations.
EXPERIENCE YOUR AMERICA
Cone-shaped fossils from the internal skeletons of
belemnites are sometimes found in this area.
Find and feel many small indentations and
bumps on the large rocks on the ground.
These are impressions of saltwater clams.
To explore a completely different type of
environment, retrace your steps to the
junction and continue down the main trail.
149 million years ago
Dinosaur National
Monument
U T A H
A R I Z O N A
C O L O R A D O
N E W
M E X I C O
© Ron Blakey, Colorado Plateau Geosystems, Inc
Where are the Stumps?
Despite its name, there are
no tree stumps in the Stump
Formation. This layer of
rock formed from a seafloor deposit that extended
over a vast area beyond
the monument. The Stump
Formation gets its name
for Stump Peak in Colorado
where the formation was
first researched in depth.
Start your fossil discoveries at the Stump
Formation by turning left at the first trail
junction. By the end of this trail spur, you will
have traveled back to about 163 million years
when this area was part of a large inland sea.
The Stump Formation reveals evidence of
an ocean environment with a large variety of
life. Fossils in these rocks include belemnites
(squid-like sea creatures), snails, ammonites,
and bones of an ichthyosaur (giant marine
reptile that resembled a modern dolphin).
This area was mostly dry and warm, similar to central Texas,
when dinosaurs roamed what is now eastern Utah.
Ten different species of dinosaurs have been
discovered in the Morrison Formation within
the monument. They range in size from
about seven inches to nearly 100 feet, with
some sauropods exceeding 50,000 pounds.
New research on non-dinosaur fossils such
as small animals, plant remains, pollen, and
insect trackways, tells us more about the
environment in which these animals lived.
Based on this research, scientists believe
that about 149 million years ago, the area
was semi-arid and warm, with year-round
streams. These dinosaurs lived when ferns
dominated the plant life, along with conifers,
ginkgo trees, tree ferns and horsetail rushes.
When you return to the main trail and turn
left, you also return to the mudstone and
clay layers of the Morrison Formation. Soon
you will leave the Jurassic period and enter
the Cretaceous period, marked by a brown
sandstone in the Cedar Mountain Formation.
Proving that paleontologists still have much
left to discover, a new species of sauropod
named Abydosaurus was recently found in
this formation in the monument.
95 million years ago
Inland Sea
Dinosaur National
Monument
U T A H
C O L O R A D O
A R I Z O N A
N E W
M E X I C O
An inland seaway reached from the Arctic Ocean deep
into North America, covering this area for millions of years.
Revised 2013
© Ron Blakey, Colorado Plateau Geosystems, Inc
Stump Formation