Day 69 (July 22). More Great Basin; Utah Canyons

From: Eli, NV

To: Green River, UT

Miles today: 344

Total miles: 14554

As I continued to ride through the Great Basin, with its rocks exposed at numerous road cuts, I became puzzled.  I don’t know much about geology, but I like it and try to learn where possible.  I kept running into rocks that I knew were sedimentary, and then rocks that were pretty clearly volcanic ash and thus igneous, and then some different type of sedimentary rock.  Then the entire process would repeat, with variations, many times.  This didn’t make much sense to me, based on my limited understanding of how mountains form.  What was the geological, historical explanation of this weird place?

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Rocks seen in the Great Basin.  Upper left: limestone, I think.  Upper right: definitely volcanic ash.  Lower left: that's shale. Lower right: I have no idea. 

I only knew of two ways to form mountains.  One way is the land gets compressed (usually from a collision), and then the rocks rise up and are folded (like a crumple zone), e.g. the Rockies.  The only other way I knew is the dissected plateau, where an area is lifted up and then water etches deep into the “surface,” which is what a good deal of West Virginia is.  Neither of these made much sense here.  So naturally, I went to the Visitor Center in the Great Basin National Park, east of Eli on US 50.  They had a display on this very subject, which taught me a third way to make mountains.  In the Great Basin, the underlying region was actually stretched by about 50 miles, not compressed.  This spreading caused uniform strata of rock to “fall over.” The upper edges became the mountains, and the lower parts got filled in with eroded debris, creating those long, flat regions in between the ranges.  In the model shown below, some of the colored layers are igneous (mostly ash, sometimes lava), and some are sedimentary.  Thus the repeated progression of rock types as I passed through the ranges. I feel slightly less ignorant.

Great Basin geology explained; different colors (left) are different rock types.  From the Visitor Center.

After leaving the GB Visitor Center, it was only a short way until I was in Utah, although I remained in the Basin for another hundred miles or more. Then, geologically, I reached the eastern edge, the Wasatch Mountains. The road basically took low passes through them, and then I was on the other side. 

The “other side” is the Colorado Plateau, most of which is actually in Utah.  If you have ever been to Utah, you have probably been to Bryce Canyon, Zion Canyon, and Arches National Park. All of these are in the Colorado Plateau.  The entire region, the size of a state, is composed of several different colors (and of course types) of sedimentary rock (deposited under water), all relatively level (not folded or tilted) but uplifted to 4000 feet elevation or more.  Then water cut deep channels, including the Grand Canyon to the south (which is actually in the Arizona plateau, but most of the strata are the same), and the work of water and ice on the porous rocks created dramatic structures.  OK.  Well, Bryce and Zion are especially cool, but the entire region is comprised of the same strata, and has the same forces of erosion working on it. It is very difficult terrain, and there seems to be only one major east-west road through it– I-70.  A view on Google maps lets you know something is up.

I-70 through the Colorado Plateau (in Utah).  Interstates are not usually this "squiggly."

The informative signs at the plentiful rest stops long this otherwise empty route between Salina and Green River (no food or gas for 109 miles) tell the interested reader that formations like the one shown below are called “castles.”  There are lots and lots of castles on this route. 

A castle (formation) in Utah.  There are hundreds of these. 

Despite having been in Utah two or three times, I had never driven this route.  I tried to only stop at the places that said “photo pull-off ahead,” but still took over a hundred pictures.  I will only show one here, as the image loses something when you put a border on it.  This is a picture of Spotted Wolf Pass, and that, folks, is I-70 running through it.  This is probably the most scenic stretch of Interstate in the US, and probably the most expensive to build. I rode this a few minutes after taking this picture.

Spotted Wolf Pass.  That's an Interstate down there!

I continued riding to the town of Green River, on the river of the same name, and stopped there for the night.  This is where I am now.  Interestingly, across the street from my motel is a park, and in that park is a sounding rocket.  Really.

An unusual display across the street from my motel.  Green River, Utah.