Category Archives: Colorado River

The Green River Formation

The World Famous Green River Formation, for oil shale, not beauty

The World Famous Green River Formation, for oil shale, not beauty

About fifty million years ago the Grand Canyon and the Colorado River did not exist.  The area was surrounded by the Wind River Mountains, the Uintah Mountains, the San Juans, the Uncompahgre Plateau, and the newly formed Rocky Mountains.  This huge area had no outlet to the sea.  The climate was similar to our current Gulf Coast, warm and moist.  During the six million years we are exploring, things changed.  Lakes formed and receded, land rose and subsided, and through all this the surrounding highlands were sending their sediment into the lakes.   

The Green River Formation is the result of all the sedimentation.  It is up to ten kilometers in depth, thinner at the margins.  At first the lakes were fresh water, but later became saline, leaving large deposits of carbonate rocks.  The trona deposits at Green River, Wyoming are some of the richest in the world.  The margins are sandstone and conglomerate interlaced with the fine silt that filled most of the basin.  The formation is rich in the fossils of the abundant life in the lakes.  They are world famous for their variety and abundance.   

There was an anoxic layer at the bottom that preserved the organisms settling there.  The lakes were abundant in blue-green algae.  The remains of the algae are the source of the oil shale deposits the region is known for.  The oil shale is there in millions of barrels, but it is expensive to extract the petroleum from the rock.  It may never be commercially viable, but the formation has been extensively studied as a result.  

Green River Formation Map

Green River Formation Map

Standing in my home town of Fruita looking north, the white cliffs behind the Book Cliffs are the Green River Formation.  The Roan Plateau is huge, but does not attract visitors like the red rock country to the south.  A huge exposure is the highlands west of I-70 from Rifle to DeBeque Canyon. 

My interest is from visiting ranchers and hunting in the Douglas Pass area in my youth.  Most of our visits were to ranches in the Green River Formation.  The elevations varied greatly.  The ranches were along West Salt Creek, but there were back country roads that went from sagebrush desert to piñon-juniper to oak brush shaly hillsides with sandstone rims to high country timber with world class mud.  In fact, the mud is world class everywhere in the region. 

Back before four wheel drive became common, there was a pile of rocks at the bottom of every big hill.  Load them in the back of your pickup, go where you planned, and unload them on the way home.  There is a network of canyons with side canyons branching off.  All of it is fine deer habitat.  My favorite places were at the head of a canyon with the wind in my face and a view of the LaSal Mountains and the Uncompahgre Plateau in the distance.  Flat, wooded country gives me the creeps. 

Access to a lot of the country is difficult.  Most of the land is BLM land, but the early ranchers homesteaded the choice land that had water.  The private land meant locked gates.  We knew some of the ranchers, family friends.  Hunting season was a big deal.  There were maybe a dozen or more people, hunting during the day and drinking and playing poker at night.  The big ranch house had a big kitchen with a wood burning stove along with the stove in the big main room.  There was a light plant in the shed next to the house.  It looked like no generator you see these days.  There were also lots of Coleman lanterns when the light plant failed.  Good times and lots of venison.  The unheated bunkhouse was upstairs. 

Douglas pass was up the main road, gravel in those days.  It isn’t that high by Colorado standards, but made up for it with the switchbacks up the head of the canyon to the summit up through that shale.  When the shale is wet, it moves.  The road trapped the runoff, wetting the soft shale, and most every spring one or more places slid.  The mountainside now is braided with old road cuts.  It wasn’t much of a main road in the 1950’s, but now there is so much oil and gas development that the road is a paved state highway that the highway department spends money on. 

The road crosses the desert above the Highline irrigation canal before it goes into the canyon.  It is on the Mancos shale, responsible for all that flat desert in Colorado and Utah that turns to grease when it is wet.  There was one hill the road went over then descended into the wash on the north side.  That meant the road was on a north facing slope for a distance.  That hill was named Coyote, because it could bite and gnaw on you if it was wet.  A bit farther north was a ten or twelve foot high rock on the side of the road, all by itself.  

The county employee maintaining the road in those days had his grader blade scrape on that rock every time he bladed the road.  It would leave a bump, so he would have to drag dirt over to level things out.  One day he got fed up and dug that rock up and moved it off the road.  It was probably a two day project, but he never had to fight that damn rock again. 

After I could drive, I ran around that desert quite a bit.  I learned how to drive a two wheel drive pickup in that greasy stuff from my father.  He was the telephone man in Fruita, responsible for maintaining the toll line as far as Cisco, Utah.  That meant navigating two ruts through the cheat grass and sagebrush.  He could put a two wheel drive pickup into places that were a challenge for a Jeep.  Rocks in the back, chains if needed, put it in second gear and putt along.  He seldom used the granny gear or used the gas pedal.  Those old Chevy sixes would just lug their way along.   

I am as guilty as any back country explorer for spending most of my time in the Rocky Mountains or the Utah red rock country, but the Mancos Shale and the Green River formation are calling me.  I just need to see if my tire chains are in good shape.  I think I will go over Douglas Pass, loop around and look the Piceance Basin over. From Rifle I will go down to Plateau Creek (my father and grandfather said platoo crick) and up to Collbran to look at the big slide.

The Colorado Plateau Part Two

 

Colorado Plateau Country

Colorado Plateau Country

There is a lot of beautiful country on the Colorado Plateau, but there is the other side.  The term many use is the stinking desert.  My home town has an annual rainfall of about eight inches.  Before the Utes were run out and ditches were dug, the Grand Valley was a sparse desert.  The irrigation projects made much of the valley green, but north of the Highline Canal is the desert.  It is a fairly barren desert, not like the Sonoran Desert with its green saguaro cactus.

Mancos Shale Soil

Mancos Shale Soil

The soil, if you can call it that, is fairly infertile, high in salts, and high in toxic selenium.  It’s called the Mancos Shale.  The Mancos Shale, called the Pierre Shale east of the Rockies, runs from South Dakota to central Utah.  It is an ancient sea floor, Cretaceous in age, of the inland sea covering much of North America.  Shale is mud rock, laid down as the sea advanced and retreated over millions of years.

The lower part of the Bookcliffs and the valley floors are Mancos Shale.  In its natural state it is a scrub grassland, supporting small populations of deer, antelope, prairie dogs, sage grouse, cottontails, and some Bison.  When the Northern European Americans arrived, they saw grazing land.  The sheep and cattle came.  The ranchers did well for a few years, but their expectations were unrealistic for such a dry area.  Soon, most of the good grass was gone, replaced by cheat grass and sagebrush.

The area between Delta and Grand Junction is a prime example.  My father, born in 1903, lived in Grand Junction after 1918.  He told me that at that time, there were extensive stands of tall bunch grasses.  They are gone.  That desert is one of the most barren stretches I am aware of.  It is hilly, so irrigation water went to flatter areas.  It is close to towns, so lots of ranchers grazed their stock on the land.

Much of the Mancos shale country is BLM land today.  In the old days, the Land Office and the Grazing Service leased land to ranchers.  There were allocations on the number of head allowed on each segment, but there was little enforcement.  The grass mostly disappeared.  Thus, the stinking desert.

I-70 from Palisade to the west of Green River, Utah is on the Mancos.  Highway Six from where I-70 veers south almost all the way to Price is on the Mancos.  Travelers on those highways have the bare Bookcliffs and the bare desert floor to look at for over 200 miles.  Their impression was what tended to keep the canyon country to the south relatively isolated.  Locals had all that magnificent country mostly to themselves.

Art in Salt Creek Canyon

Art in Salt Creek Canyon

The a uranium and oil and gas booms of the 1950s built a large network of roads and opened the canyon country up for tourism.  Those flat deserts remain empty, along with the mostly shale country of the Bookcliffs and the Tavaputs Plateau to the North.

When I went to Arches in the 1950s, we drove down two tracks winding through the sand.  This year during the height of the season, cars were lined up literally for miles.  Canyonlands National Park is also crowded, people lined up.  I remember going there and often seeing no one.

From Green River to Hanksville is mostly flat, dry desert, with 70 miles from the highway turnoff to the Maze District Ranger Station in Canyonlands.  The greater part of Navajo country in southern Utah, New Mexico, and Arizona is fairly flat desert.  Monument Valley is flat desert that happens to have some rocks sticking up.  Have you ever driven from Albuquerque to Flagstaff on I-40?  Flat desert.

Henry Mountains

Henry Mountains

The Colorado Plateau does have some other features.  Mountains, tall, green, and wet, supplying water to the desert.  Three ranges of mountains, the La Sals near Moab, the Abajos, known to locals as the Blues, and the Henry Mountains, near to nowhere.  The La Sals are the tallest, over 12,000 feet.  The Abajos and the Henrys stretch to 11,000 feet.  They stand in contrast to the red rock country surrounding them, and provide a welcome relief.  People go there in summer to cool off and enjoy the wildlife.

Geologically, the mountains are Laccoliths, formed by a neck of molten magma rising to a weaker junction between two layers of sandstone.  At that junction the magma moves laterally, forming a mushroom shaped dome of igneous rock in the domain of sandstone.  The overlying strata usually erode away, leaving the igneous core.  The Henrys are the type location for Laccoliths, being the subjects of the earliest study, and displaying the domed shape.

Salt Creek Canyon

Salt Creek Canyon

The three ranges are important to ranching, providing water, hay farming, and a summer range, with the stock wintering on the desert.  Salt Creek, draining north from the Blues, has a canyon with year-round water, arches, and Ancestral Puebloan ruins and rock art. The canyon also provides access to a park in the midst of the Needles District of Canyonlands.  I like that park because it was never grazed.  It provides a look at the land before cattle came, trampling or eating everything, mangling stream banks, and bringing alien species like cheat grass.  No I won’t tell you where it is.  Go look for yourself.

 

The Colorado Plateau Part One

Colorado Plateau Scenery

Colorado Plateau Scenery

I am a child of the Colorado Plateau.  I was born and grew up in Fruita, Colorado, and still think of Fruita as home, although I have lived along the Front Range of Colorado most of my life.  The Grand Valley of the Colorado River is near the Grand Hogback, the eastern extent of the plateau in that area.  The Grand Valley is green due to irrigation, but the annual precipitation averages around eight inches a La year, fairly typical of the Plateau.

I am sure that the center of the universe (well, my universe) is somewhere within 100 miles from the confluence of the Green and Colorado rivers.  It is fitting, therefore that the Plateau is somewhat unique geologically.  All those striking layers of varicolored rock formed into spectacular scenery by the work of the Colorado River and its tributaries are relatively undisturbed compared to the Plateau’s neighbors, the Rocky Mountains,  the Basin and Range, the Wasatch and Uintah mountains and the  Mogollan Rim in Arizona.   Pretty neat neighbors, eh?

Those places have been folded, faulted, stretched lifted, collapsed, and otherwise deformed.  The Plateau, on the other hand has remained relatively stable through much of geologic time.  It is this big slab, poked, lifted, twisted, drowned, buried, and eroded several times but still mostly intact.  There were just enough deformation and intrusion to make things interesting.

The reasons for this stability are still somewhat controversial, bit have to do with the Pacific Plate coming our way and north at about the rate your fingernails grow, and the North American Plate headed west at about the same speed.  At different times they have behaved in different ways that, coupled with the somewhat thicker crust under the Plateau, have resulted in this unique region.  I don’t have the space or understanding to explain all those processes, but we can see the result.

An interesting fact is that the entire plateau seems to be rotating clockwise as the Pacific Plate grinds along northward.  That movement is also what is pulling the Basin and Range province apart.  Don’t look for any big changes next week.  This process is really slow.  While all this plate movement is going on, our friends the Green and Colorado rivers just keep digging.  On rare occasions you can see the digging, when there are exceptionally big thunderstorms during the summer monsoon.  A lot of stuff goes into the rivers then.  Today, Lake Powell is catching it, and will become one huge mud flat until the dam eventually fails.

Looking at all these processes requires a different sense of time than how we live from day to day.  In geologic terms, sixty million years (60ma) is relatively brief.  We think of our world as stable (unless you live in the Bay Area) but in truth, everything is on the move, it is just a bit slow.

Upheaval Dome

Upheaval Dome

The Colorado River will eventually bring the entire plateau down to sea level.  Look at Grand Canyon or any of the tributary canyons to see how it works.  My favorite is the San Juan.  Some fine canyons and not as cluttered up with people.  Another place to see the processes of change is Upheaval Dome in Canyonlands National park.  A great big rock came along and smashed down, forming a huge crater and shaking everything up for a long way around.  You can see rocks turned to waves from that hit all the way to Dewey Bridge.

That big crater tried to form a lake, but it is dry there.  The water did make its way to the river, cutting as it went, and now the crater has an outlet.  The crater will get bigger as the cliffs erode back until it is just a depression, then, gone.

There is a plug of gypsum in the crater.  When all that rock was blown out by the impact, the pressure on the stuff under the crater was lowered.  Some of that stuff down there is salt, known as the Paradox Formation, which can flow.  The salt goes into the river, but gypsum isn’t quite as soluble and there it is.  The salt is from an ancient sea that alternated between filling and drying up as sea level rose and fell.  That left a lot of salt which was then buried under a lot of rock.

The Dolores River Leaving the Paradox Valley

The Dolores River Leaving the Paradox Valley

That salt moving around and being dissolved is responsible for much of the scenery in the Moab and surrounding areas.  As it dissolves, some of the overlying rock drops down, creating some fairly large valleys.  Paradox Valley, Sinbad Valley, Lisbon Valley (uranium, oil, and gas), Spanish Valley (Moab), Castle Valley, Fisher Valley, are all big grabens.  They are big blocks that dropped down as the salt leached away. Paradox Valley and Spanish Valley have rivers coming out of a canyon on one side, and going across the valley into a canyon on the other side.  Moab has the Colorado, Paradox has the Dolores.  That makes for some fine scenery.

Paradox Salt Disrupting Things

Paradox Salt Disrupting Things

The fins and arches in Arches and Canyonlands come from the same process on a smaller scale.  All that magnificent scenery is a result of that ancient sea floor full of salt being buried by a colorful succession of rocks that the rivers and the wind could work on.

An exception to the salt influencing the process resulting in fins and arches is Rattlesnake Canyon in Colorado near Fruita.  The river is solely responsible for the work.  The arches are just as cool, and not all full of people.

Next time, some of the other interesting things about the Colorado Plateau, one of the most interesting places on the planet.