Roger Weller, geology instructor
Fred E. Thomas
GLG 101- Fall 2005
GEOLOGY AT FLAMING GORGE,
area discussed is located between Vernal,
Vernal is at coordinates N40 27.331; W109 31.726.
Flaming George is part of the Flaming Gorge National Recreation Area, a 207,363-acre parcel that is part in
The whole area is on the
“Colorado Plateau” which has risen almost straight up to elevations as great as
10,000 feet. The Flaming Gorge area lies
on the very northern edge of the Colorado Plateau. The Plateau appears to end in the Vernal
area. The Plateau is made up of many
smaller plateaus each a few hundred feet higher or lower than others. Faults and folds result in a rich geological
history of the area.
Colorado Plateau from “Pages of Stone”, The Mountaineers Book by Halka and Lucy Chronic.
Traveling north from Vernal, on US 191, there will be seen markers naming the various earth and rock formations as seen from the road. They start with the Cretaceous Period. [The Cretaceous, Jurassic and Triassic are within in the Mesozoic Era of the Phanerozioc eon] consisting of the Mancos Formation, the Frontier, the Mowry and Dakota formations. The Mancos is the youngest and composed of clay that settled to the bottom of the sea which covered the area. Many fossils are found in these strata. Next is the Frontier in which for millions of years tropical plants were deposited by a river delta and then buried. The pressure and decomposition formed coal beds. Calcite building around fossils formed rocks or “cannonballs.” Next, the Mowry formation is about 100 million years old and is composed of shale (clay and volcanic ash) left by an ancient sea. In the strata is found fossilized fish scales and bones. The last formation seen here in the Cretaceous Period is the Dakota. This formation results from streams flowing into the ocean transporting rocks and soils to this area. Trees and plants growing along these streams are now petrified and contained within the deposit. The formation of the Dakota took place about 110 million years ago.
few miles further north on US 191 the Jurassic period formations are
found. The Morrison, Curtis, Entrada,
the Curtis formation the seas left and the land became desolate. Neither plants nor animals lived here. Winds laid down layers of sand and dust. This was about 150 million years ago and is
the Entrada Formation. During the next
GOOGLE EARTH – Along US 191 to Flaming Gorge from Vernal North
In the background is the Navaho Sandstone and the “ships” that resulted in the “Red Fleet” name.
In the same period, Jurassic is the Navajo Formation. The red rock in the background of the above picture is Navajo sandstone. This layer was formed by large sand dune where the sand was cemented by silica or lime. This layer is said to have been formed over millions of years.
should be understood that in different geographic areas – differing formations
are found. A few miles east of Vernal
and the Flaming Gorge area is the
Continuing north along US 191 we leave
the Jurassic period formations and enter the area of the Triassic. This is still in the Phanerozoic Eon and the
Mesozoic Era. During the Triassic period
the area was covered by lakes and low lands where a crocodile like reptile was
living. Only the teeth have been
found. The strata contain mud pebbles,
mud cracks and ripple marks. Geodes are
found there with cavities lined with calcite or quartz crystals. In the very early part of the Chinle
formation there is the Shinarump member (this area had pine trees that grew up
to three feet in diameter and forty feet tall).
The trees were of the Araucaria species, as found in
US 191 passes through a section of the Permian period and the Park City formation. This formation is rich in phosphate. A large mining operation can be seen from the highway looking westward. The phosphate was formed by decomposition of marine animals.
leaving the Permian Period and the
Next in time, going further into the past, would be the Devonian (408 to 360 million years ago), the Silurian (440 to 408 million years ago), and the Ordovician (505 to 440 years ago) . These periods are missing. It is called a “unconformity.”
Next we come to the Cambrian Period (540 to 505 million years ago) of the Phanerozoic Eon – the Paleozoic Era. The only formation left of this period is the Loddore. Again a sea was involved and a mud and sand strata in which trilobite’s found their grave. Evidence is the fossilized shells of the trilobite and other ancient marine animals.
the highway passes over the oldest part of this area. It is called the Uinta Mountain Group formed
during the Precambrian Period. This is
of an older Eon – Proterozoic extending from 2500 to 540 million years
ago. During the early part of this eon
the first large continents appeared.
Toward the middle of the eon the continents were grouped closely together
in almost one land mass. Salt was washed
off the lands, algae plants produced oxygen and in time more complex life
began. This Uinta Mountain Group of
about a billion years old is three miles thick.
If you went back to Vernal (south on US 191) and dug down to reach this
stratum the hole would be two and a half miles deep. The strata that were
deposited in this thirty mile trip from Vernal to the beginning of the Uinta
Mountain Group were lifted vertically while retaining a horizontal
layering. This mountain was then eroded
away leaving a pathway traveling toward the center of the earth. While continuing northward passing over the
Flaming Gorge Dam and into the State of
PAGES OF STONE, Geology of the Grand Canyon & Plateau Country National Parks & Monuments, second edition, The Mountaineers Books, by Halka and Lucy Chronic.
THE FIELD GUIDE TO GEOLOGY. Facts On File, Inc/ Diagram Visual Informatiion Ltd. , 1998.
WILDLIFE THROUGH the AGES – FLAMING GORGE – Uintas National Scenic Byway. Compiled by Dinosaur Nature Association and the Utah Division of Wildlife Resources.