Category Archives: Utah

Plate Tectonics

Western Colorado’s Grand Valley

As a Western Colorado Native, having lots of geology looking down on me sparked my interest in the field.  I have to know, so knowing how the Bookcliffs, Grand Mesa, and the Colorado National Monument got there stirred my curiosity.  Plate Tectonics is responsible for that stuff poking up all over the place.

Back in the Permian when I took geology at Mesa College, the orthodox explanation for mountain building was something called isostasy.  Push down in one place, and something will pop up nearby.  New Orleans and the Mississippi Delta is sinking under the weight of all that mud coming down the river.  New England is rising a little because that heavy glacial ice sheet melted.  Geologist tried to make isostasy work in places like California with little success.

The early twentieth century saw some new thinking.  Alfred Wegener proposed that continents move around on our sphere.  He was laughed at when he gave papers on the idea.  Yes, Africa and South America look like they once fit together, but how can an entire continent move?  That is a lot of mass to be sliding around.

In the nineteen sixties new thinking started to change attitudes.  Why are there identical fossils on the African and South American coasts?  The real game changer came when oceanic exploration found the mid-oceanic ridges with young basalt near the ridges and steadily getting older farther away.  The only explanation was a spreading seafloor.  Things are on the move.

After college I subscribed to Scientific American magazine.  It seemed like a new article appeared every month explaining how physical features are the result of magma (molten or hot and plastic rock) on the move.  There are seven big (North America, Asia) plates and a number of smaller ones being affected by the rock coming from that spreading seafloor.


As the oceanic sea floor impacts the boundary of a continent, something has to give.  The more dense seafloor basalt tends to dive under the continent.  They can form trenches almost seven miles deep next to a subduction zone where the plate dives under the lighter rock of a continent.  The subducting rock is wet, and changes chemically forming lighter rock that often belches up as volcanos.  Earthquakes occur as the plates bump against one another, dip, or slide.

The island arcs off Asia are the current example.  Java, the Philippines, Japan, New Guinea are all volcanic islands getting ready to smash into Asia.  India already has, creating the Himalayas at the suture.  Lots of shaking there, too.

Around 1.75 billion years an island arc docked (yes, geologists use that word) on the Wyoming Craton.  The craton has some rocks as old as six billion (abbreviated as 6 ga) years old.  Many of the rocks are around 3 ga.  The oldest Colorado rocks are around 1.75 ga.  Just outside Morrison, Colorado is the Great Unconformity.  The red rocks are about 60 ma (million years).  The dark gneiss and schist just barely up Bear Creek canyon are those 1.75 ga guys.  Lots went on between those dates, but there it is all eroded away.

Snowy Range, formed by Colorado smashing into Wyoming

The Snowy Range in Wyoming is a result of the join-up.  The coastal ranges in California that like to shake and burn and belch fire and rock formed from the collision of the Pacific and North American plates.  As you are probably aware, L.A. is headed for Anchorage.  Don’t worry it’s going to take a while.

The Rocky Mountains are kind of a strange story.  Usually mountain building occurs at plate boundaries, like the Andes and the Cascades.  What is known as the Laramide Orogeny that created the Rockies happened about 800 miles inland.  The idea is that for some reason about 80 ma the pacific plate scooted under the lighter continental rocks before diving. The Rockies came up a bunch, the Colorado Plateau, my homeland, not so much.

The Rockies are now sitting still but the plateau is moving clockwise, pulled by the pacific plate sliding north against and under the north american plate at the continental boundary, as things should happen.  The Basin and Range province, Nevada mostly, is being pulled apart.  For some reason the Colorado Plateau wants to stay in one piece while western Utah, Arizona, and Nevada are coming apart.

All this motion is happening at about the rate your fingernails are growing.  It doesn’t seem like much, but after a few million years we are talking big moves.  Stay tuned.

My favorite book on these topics is Annals of the Former World, by John McPhee.  It is a big book composed of sections covering the territories along I-80.  Great reading.

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.

Boise Road Trip Part Two

In the first installment I got us as far as the Wasatch Front, and warned of the future apocalypse-earthquake waiting to happen there.  I was on the way to Boise, and needed gas.  I took an exit and pumped gas, moved the Tacoma to a parking spot, and went inside.   

Pried Open Sliding Window

Pried Open Sliding Window

When I came out I saw my keys on the seat.  Oops.  No spare key.  I have done this before, and it usually means breaking a window. The Tacoma has a sliding rear window, useful for ventilation in good weather.  I borrowed a screwdriver from the guys parked next to me.  I figured that was the cheapest window to replace if I had to break it. 

The window has a plastic latch and I pried between the panes there.  The glass bent and the latch popped open.  I have tried those magnetic key holders and they always disappear.  I’ll figure out a stash spot sometime. 

On the road again, I drove through some arid hilly country-cow country, in the wind.  I have always thought that Wyoming is the wind capital, but the wind has to come from somewhere, I guess it is northern Utah and Idaho.

Driving on north, near the Snake River it is irrigated farmland, reminding me of home.  I was getting tired and stayed in Twin Falls.  It’s not that far to Boise, but when I am tired I lose concentration, not good at 70 mph. 

Oregon Trail Ruts

Oregon Trail Ruts

The Oregon-California Trail parallels the Snake in that region, so I went rut hunting.  The Snake runs through a gorge in the Snake River Plain, so the trail left the river if there were alternate water sources.  Those hills Idaho people call mountains also run parallel to the Snake a few miles north, and the trail ran there away from the river. Water was available from springs and creeks at the base of the hills.  The water is gone now, victim of all the groundwater pumping by farmers.  

 The ruts are there, as well as the ruins of an attempt at a resort in the early part of the 20th century.  I like following the trail, thinking about what it was like for the emigrants, traveling 8 to 10 miles per day, hoping for a better life at trail’s end.  Many found the better life, many did not, and many died on the way.   

 On to Boise, seeing people I care about, and searching for Basque food.  Headed home it was back to the Wasatch, then U.S. 40 east.  I had never been west of Vernal, so it was new country for me.  The highway rises through the Wasatch to Heber City, a nice town that reminded me of our Eagle River valley, with all the businesses supporting the ski resorts.  The Wasatch Mountains are rhe easternmost range of the Basin and Range Province.  The Basin and Range is being stretched as the Pacific Plate scrapes northward along the North American plate. 

Uintah Mountains From US40

Uintah Mountains From US40

Leaving the Wasatch Mountains, we are back on the Colorado Plateau, with its northern boundary, the  Uintah Mountains.  The Uintahs are unique among North American mountain ranges, as they run east-west.  They were uplifted at the same time as the Rockies, but I can’t find a good explanation of why they run east-west.  There they are, and I drove east with mountains on the left and desert on the right.  Come to think of it, the Book Cliffs and the Tavaputs Plateau also run east-west, but they aren’t called mountains because they are only 8000 feet high.  The Uintahs have two thirteeners.   

 Highway 40 runs between the Uintahs and the Tavaputs.  The Uintahs are important to the Salt Lake area, providing water for the growing population.They are also pristine, mostly roadless.  The glaciers are gone, but they left dramatic peaks and broad mountain valleys.  The core is the High Uintahs Wilderness,the rest Forest Service land providing summer range for sheep and cattle.   

Next, Vernal. It reminds me of Cortez, Colorado and not in a good way.  It is, however, a good jumping off spot for a lot of interesting country. 

Green River Campground, Dinosaur National Monument

Green River Campground, Dinosaur National Monument

The eastern end of the Uintahs have Dinosaur National Monument, with its fossils and the amazing canyon of the Green River.  I was camping down on the river one time a few years ago.  My neighbors in the campground had some dogs they were letting run loose.  I warned them about the skunk I had seen.  Early next morning they learned about skunks and dogs and I got to hear some morning howls.  I am glad I wasn’t in their car on the way out. 

Maybell, Colorado is next, a ranching town isolated enough that the natives retain the western drawl, a dying accent.  On to Craig with its coal controversy, then Steamboat on the Yampa.  Pretty country.  Then, drive over Rabbit Ears and Berthoud Passes, down to I-70 and a traffic jam.  That meant I was close to home.

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.