Crash Course in Geology

"Is this a hogback?"

I had just moved to Grand Junction, Colorado, a town with some of the most spectacular scenery anywhere. Part of that scenery is the Colorado National Monument, an area of the Uncompahgre¹ Uplift that has thousand-foot cliffs of mostly red rock and canyons almost as deep.

I decided to go hiking. I unknowingly picked the toughest trail in the whole place: the Liberty Cap Trail.

The grueling - and terrifying - Liberty Cap trail, Colorado National Monument

Yes, it literally goes up the face of that cliff, following little, narrow ledges. And it became terrifying! I finally turned around at point 9.

So the next spring I decided to write a story, with photos, about that hike. That is not today’s story; I’ll have to fish it out of my archives sometime and publish it here.

Today’s story begins with the portion of the trail that is a dashed red line between points 4 and 5 that are behind that triangular chunk of rock that is not the same as the others. I wasn’t that curious about what it it was; all I wanted to know was what the correct word is for that thing, so I could use the correct word in my story.

Over on the other side of the Rockies, 250 miles away (by road), is a feature that runs the entire north-south width of Colorado they call “the hogback.” This thing kind of reminded me of it. “So,” I mused, “is this thing called a hogback? Can I use that word?” I started diving on the Internet.

Somewhere around 3 am, I came up for air. I had learned more about geology than I ever intended to. And I was hooked.

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A flashback to 45 years earlier:

I was first exposed to geology by a gifted instructor / naturalist who worked for the Oregon Museum of Science and Industry during the Space Race when I was a teenager. Science was very important at that time, and got lots of funding.

Back in those days, he conducted a “Science Tour” for a bunch of science-y type kids where we all rode in a really nice school bus around the Pacific Northwest for a week or two in the summer, camping out and looking at science stuff. It was a different trip to different places each year, repeating every third year.

As a naturalist, he gave us all of it: botany, ornithology (his specialty), herpetology, ecology — and a whole lot of geology. We saw the Tetons. We saw Yellowstone. We saw the Great Salt lake. We saw the Hot Stuff at Mt. Lassen. We saw Oregon’s High Lava plains province. We saw the Columbia Gorge.

It was too much to absorb. I never retained any of it, but I was fascinated.

His name is Jim Anderson and he’s in his nineties now [EDIT: now deceased - see footnote²]. If you know or meet him, say “Hi.” I think about him every time I learn something new about geology. Indeed, a few years ago he loaned me a signed copy of the original book about Oregon geology by The Old Man himself: Thomas Condon. Man, I treated that book like a Rembrandt, or a Stradivarius. I knew what I was holding. I read every word, turning the pages very carefully, and got it back to him before something bad could happen to it.

There is so much to know, so many stories to learn from the rocks. I really don’t understand how anyone can learn enough to get a geology degree in only four years.

And now, back to the story.

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I had learned the names of the six formations in this photo, and the distinctive look of each. I wasn’t sure how to pronounce them, but I was able to recognize them and remember their names. Finally, I had learned some little bite-sized pieces of a field that had fascinated me all my life - pieces that I could remember and recognize when I saw them.

I had learned how this cliff had formed, and roughly how long ago. The layers, in order from bottom to top, are:

1. X: Colorado’s basement rock. Black 1.7 billion-year-old Proterozoic rock that is very rough, tough, and almost doesn’t erode. This stuff underlies the entire state except for a two-mile-wide sliver next to Wyoming.

2. C: Chinle Formation. Bright red and crumbly; very weak rock that erodes instantly. Laid down from 220 to 200 million years ago in the late Triassic.

   That’s right, we go from 1.7 billion year old rock to 200 million year old rock. There is one and one-half billion years’ worth of rock missing here. This is called an “unconformity.”

3. W: Wingate Sandstone. A yellowish-red rock that is hard enough to form tall cliffs. From sand dunes that piled up 200 to 190 million years ago in the early Jurassic.

4. K: Kayenta Formation. In most parts of the Monument, this is a relatively thin layer that is only a few inches to a foot thick. It is exceedingly tough; like concrete. The Liberty Cap, up on top and the reason for the trail, is made of a particularly thick glob of this stuff. It was laid down 190 million years ago.

5. E: Entrada Sandstone. Deeper red than the Wingate; not as red as Chinle. Not as tough as Wingate, but can still form cliffs. While the Wingate erodes cleanly, making sheer walls hundreds to thousands of feet high, this stuff makes lumps and sometimes smooth walls that are sloping. It is mid-Jurassic: 180 to 160 million years old. Above the Entrada Formation is the Wanakah Formation. It exists in the Monument, but there isn’t any of it in this photo.

6. M: And finally, above all of these others, is the famed Morrison Formation. Where all of the dinosaur bones are. It is sands, muds, clays etc. that are various colors, none of them red, that was deposited by streams and shallow lakes 155 million to 148 million years ago in the late Jurassic.

But wait! Why is the Morrison, and part of the Kayenta, at the bottom of the photo? Heh heh - that, my friend, is what kept me up until three in the morning: we are looking at an uplift.

All of these layers, and more — such as the Mesa Verde Group and the Mancos Formation, lay here, undisturbed, for another 75 million years, building layer upon layer of mud, gravel, sand, you name it…

Until two crustal plates collided where California is now, starting about 75 million years ago. The Farallon Plate, under the Pacific Ocean, was moving east and refused to stop moving when it hit north America. For the next twenty million years, it pushed and pushed and pushed North America as pressure built up under our continent. Finally, North America began to crumple like a fender in a head-on collision. The Rocky Mountains started rising some thirty miles east of here, and the Uncompahgre Uplift - this thing in the photo - “popped” straight up along some old faults about 1200 feet above everything else, starting right here and going about 90 miles to the southeast. Okay, the “pop” took millions of years, but it popped. This event is called the Laramide Orogeny³.

Everything was lifted so high that the Proterozoic basement rock was lifted up to ground level. The upper layers — the Mesa Verde Group, the Mancos Formation, most of the Morrison, and some of the Entrada sandstone — were worn off down to the tough-as-concrete Kayenta Formation.

In some places, water was able to finally erode through the Kayenta to the much softer Wingate sandstone and the even weaker Chinle mudstone, and carve the magnificent canyons of this National Monument.

So in this photo, the camera is standing on top of the Morrison Formation, looking at a cliffside of much older rock that was pushed up from the deep, and if you go up on top you’ll see small patches of the Morrison up there.

The little feature that I wanted to call a “hogback” is a remnant of super-tough Kayenta Formation that was bent upward as the rock under it pushed up through it. Kind of like the way an old “churchkey” can opener bends a triangle of the can’s lid when you open it.

And I learned all that in one night.

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Epilog: A few weeks later, I was up on the Monument again, with my camera, going “Aha! There’s the Wingate layer! There’s the Chinle! There’s the Entrada, oh lookie! here’s a couple of inches of Kayenta under it!” when a busload of high school kids unloaded and I listened as their teacher told them what they were looking at. I listened especially carefully at how the formations’ names were pronounced.

What I didn’t know at the time, and will always regret not knowing, was that he was the husband of one of the authors (a mother-daughter team) of the four Roadside Geology books for the Four Corner states: Colorado, Utah, New Mexico and Arizona.

Yes, those two women, whose work I deeply admire, lived right there where I did! And I didn’t know it until after both of them, and the high school teacher husband, had all passed away.

One more thing: I think the correct name for that little triangle of Kayenta stone at the beginning of this story is “fin.” But after all these years, I still don’t know for sure.

1. A Ute word that means “Rock that makes the water red.”

2. Jim Anderson passed away in September of 2022 at the age of… I don’t remember but he was in his nineties.

3. The Laramide Orogeny, if I understand this correctly, ended when the Farallon Plate finally started subducting (sliding down underneath) North America, to get re-melted in the Hot Stuff down below the crust. It is completely gone now, except for one tiny corner off the coast of Oregon/Washington/British Columbia. That little piece was named the Juan de Fuca Plate before anyone discovered that it is actually the Farallon.