Geological Mementos

Memento (n.): an object kept as a reminder of an event or person.

My knick-knacks are dominated by rocks. But they're not just rocks. For in addition to sand, silt, quartz, feldspar, anorthosite and serpentinite, they contain memories.

Some are mementos of events: magma almost but not quite reaching the surface; raging rivers carrying debris from disappearing mountains; a rift tearing the continent, fortunately stopping in time to keep the country whole. (I'm exaggerating—it ceased hundreds of millions of years before the colonies left England.) Others remind me of people: early explorers of the American West; pioneering geologists; 19th-century naturalists; today’s geo-bloggers.

Tired of unappealing weather and cabin fever, I decided to make portraits of these rocks so I could enjoy the memories they trigger. (Note re scale: Lady Liberty's portrait is an inch across, 2.5 cm.)

“Hillers trachyte is a pale gray paste with large white crystals of feldspar and crystals large and small of hornblende.” Grove Karl Gilbert.

In 1869, while traveling down the Colorado River, John Wesley Powell spotted an unnamed cluster of peaks in the distance, which he christened the Henry Mountains. He presumed they were volcanic. Volcanic mechanisms were a hot topic at the time, so he sent the great pioneering geologist, Grove Karl Gilbert, to investigate. Gilbert discovered the mountains were not volcanic. In fact, they didn’t match any type of uplift then known. He concluded the Henrys were created by shallow intrusions of magma. He would describe and name this new type of uplift, calling it a laccolith.

In 2012, I camped where Gilbert had camped, at the base of Mount Hillers. I hiked up the slope to look at sedimentary strata tilted nearly vertical by intruded magma. A piece of “Hillers trachyte” went home with me as a memento.

South side of Mount Hillers.

Large crystals mean magma cooled underground rather than on the surface, as would be the case for a volcano.

• • •

Igneous and metamorphic stones pose on a sandstone boulder.

Three years ago, while walking up a draw in the sandstone country of eastern Utah, I was surprised to find rounded polished stones made of igneous and metamorphic rock. What are they doing here?! I was even more astounded when I read that they came from the ancient Uncompahgre uplift, which hasn't been around for at least 80 million years. These stones are ghosts of mountains past.

Enchanted by their story, I returned last year and followed the Cutler Formation south almost to Arizona. There, far from the source, the Cutler is made of sand and silt instead of cobbles. On the way home, I stopped near Gateway, Colorado, where the Cutler includes cobble/boulder conglomerates, indicating the source had been close by. I was standing on the "slopes" of the ancient Uncompahgres! I took home several ghostly mementos.

Coarse conglomerate deposited on the slopes of the Uncompahgre uplift.

• • •

The deceptive Uinta sandstone.

A billion years ago, the supercontinent Rodinia, which included North America, was coming apart. A tear ran east from the vicinity of today’s Salt Lake City. It eventually failed, but streams continued to fill the rift valley with sediments to a depth of some four miles! By the 1870s, it had become a sandstone that fooled the great geologists—Hayden, King, Emmons and Powell. None had expected to find sandstone that old (Precambrian).

It fooled me too. The cores of our mountain ranges usually are made of granite and metamorphic rocks. I thought maybe the mileage in the guidebook was wrong.

This is the Precambrian core of the Uinta Mountains?!

Layers of sediments deposited in a rift that once threatened to split the continent.

• • •

Sparky contemplates his humble role in the universe.

On my drives from Laramie to the West Coast, I’ve stopped a half-dozen times at the Lunar Crater area in central Nevada. I like to camp in the wide open country there, free of crowds and regulations. Usually I hike, and take photos of the amazing landscapes. But one time I set out in search of mantle material in a lava field (the mantle is the molten layer beneath the Earth’s crust, miles below the surface).

Volcanic magma sometimes carries up pieces of the mantle. I was looking specifically for olivine—greenish and a bit translucent. I think I found some. (I used Geology Underfoot in Central Nevada as a guide).

Green olivine, with pale plagioclase and dark pyroxene behind.

The Black Rock lava flow.

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• • •

Strolling down a river, atop a ridge.

My most recently-acquired geological memento is the lithified remains of a river. Camels, rhinos and ruminating hogs used to come here to drink, 19 million years ago. Now a trail follows the river bed—on top of a ridge! In other words the valley bottom now stands high, thanks to topographic inversion.

The “little gray potatoes” are calcified silt nodules.

Silt nodules and sand, with bits of quartz from the Rocky Mountains. Not until I took the macro shot did I notice the tiny lichen "cups" (upper left; click on image to view).

• • •

And finally ... a rock wall?

The summit?

No.

This round green rock—serpentinized harzburgite—is the most popular of my geological mementos. Friends pick it up, surprised at its heft. More than one has noted “it looks like a brain!” It's a memento of two different events. One is the creation of the California Coast Ranges—a crazy geological story which no one fully understands (or even close?). Somewhere in the process, mantle rock was squeezed up to the surface, becoming serpentinized en route.

The Big Sur Coast, land of dreams and mystery. Photo by R. Koeppel.

The elements took their toll—the green rock was weathered and broken. A fragment traveled down an ephemeral river, almost reaching the Pacific Ocean. But I intercepted it. That’s the other memorable event.

I dug the boulder out of the sandy bed of the Santa Maria River, shortly before meeting a man pushing a bicycle. “Buenos días” he said, looking at the rock. “Piedra grande verde” I replied. He smiled and continued on.

• • •   • • •

Notes on Gear

Aside from camera and tripod, the setup I used for rock portraits was simple and cheap. The light box is home-made, following Amanda’s instructions. The sun shining though a window provided light. I put the box on a music stand, with the desk almost flat. It was easy to raise, lower and tilt … except for the heavy serpentinized harzburgite brain which collapsed the stand to its lowest position. I had to adjust the tripod instead.

The dogs found this rock portrait stuff quite boring.

Old Friends (tree-following)

My circle of close friends includes two trees. This may seem odd, but it’s impossible to follow a tree for a year without become friends! It was Lucy Corrander who started these relationships, when she invited anyone with an interest to choose and follow a tree, and report on it monthly. That was several years ago. We haven’t quit. Now the gatherings are kindly hosted by the Squirrelbasket (read the latest news here).

Last month I announced I would follow a juneberry in 2016, once I found one. So far, snowy weather has limited my search. An excursion to potential habitat in Vedauwoo Glen was unsuccessful, but still fun.

We had the picnic area all to ourselves!

So for this month, I’m reporting on my old friends.

Old friends Sparky and the cottonwood tree (preparing to estimate height).

The cottonwood I followed in 2014 grows on the bank of the Laramie River, just a short walk from my house. I see it almost daily. I never did decide if it’s one tree or several (multiple trunks) nor its exact identity. At least one of its parents must have been a narrowleaf cottonwood (Populus lanceolata), but maybe this is a hybrid, with genes of the Plains cottonwood (P. deltoides). The hybrid is common in this part of the Rocky Mountains—common enough in fact to have a name: lanceleaf cottonwood (P. X acuminata). Backcrossing has produced everything in between, most frequently narrowleaf X lanceleaf. In other words … it’s a taxonomic mess.

Even in the middle of winter, I make my daily trek through the cottonwood forest along the river … as I did this morning to see how the tree was doing. Walking through the snow and bare trees, I think about the trappers who spent the winter there in 1831-32. They grew fat on bison, elk, deer and pronghorn antelope, but their horses wouldn’t eat the inner bark of these cottonwoods and so starved. The men realized too late that they had camped in the wrong kind of cottonwoods—the bark of narrowleafs (and the hybrids) is bitter.

I switched to black-and-white; it was that kind of day.

Old and new friends (Emmie in foreground).

Lots of buds up high, waiting patiently. Only three more months ...

At the base of the trunks is a secluded spot where elves and fairies gather.

The shredded plastic bag that was caught on a high branch in 2014 is gone. But now someone has flagged this tree. What does it mean? A university student’s study?

• • •

Last year I stumbled upon a willow growing in a nook in the wall of a small limestone canyon, shaded by junipers. I was surprised to find it in that dry rocky canyon. Furthermore, it was blooming—on February 23, in Wyoming, at 7200 feet elevation! I had to follow this tree and learn more.

Male pussy willow in bloom; February 23, 2015.

The silvery catkins emerging from the dark buds revealed it to be an American pussy willow (Salix discolor), specifically a male. These willows are famous for blooming very early. When I returned from vacation in late May, it had leafed out. Then in July I discovered how it survives. After a hard rain, a waterfall was cascading down the wall behind the willow. The pool at the base stayed almost a month, long after the waterfall was gone. This site is not as dry as it looks!

Pool at base (July 2015), possibly a swimming hole for elves and fairies!

The willow isn't as convenient to visit as the cottonwood. I have to drive across town, and walk about a half mile. And now it’s cold, snowy and windy. Who wants to walk in 30 mph winds?! But the sun is shining! But it’s cold! But the willow might be blooming! … that decided it.

Looking up Willow Canyon .

Hoping to see wild flowers in February, I crossed the snowy prairie, turned towards Willow Canyon, and post-holed through snow up the draw to the willow. There I found …

… the willow with it's canopy swaying and twigs dancing against the sky. Even in the canyon bottom the wind was blowing. I looked close and found white hairs emerging from a few of the dark buds—the first flowers of the season, on February 6! They were wonderful to see, but impossible to photograph. I collected two twigs and took them home.

Willow flowers are hardly showy, but I love this “bouquet”—it’s so nice that the flowers are emerging, confirming that spring will arrive again.

When I collected the twigs, a bit of white hair was visible at the tips of two buds. Now 24 hours later, one of the buds is beginning to bloom vigorously (relatively speaking), and a third is opening.

When male pussy willow catkins (flower clusters) first emerge, they are silky and suggestive of cats’ feet.

Male pussy willow flowers (lower right) have several stamens, a nectary, and a bract with long silky hairs.

Britton and Brown 1913 (via USDA Plants Database).

Tree-following ... let's do it!