Sunday, January 8, 2017

A New Year, a New Tree

Dreaming of a subtropical Wyoming (source).

The New Year is upon us, as is the January gathering of tree-followers, kindly hosted by The Squirrelbasket. Many of us have chosen a new tree to follow.

In Laramie, choosing a tree this time of year is not so easy. Our trees either lie dormant until April (willows, cottonwoods) and May (most others), or they’re evergreen conifers that don't change much through the cold season. Last month, I checked out several candidate trees in the Williams Conservatory, non-natives new to me that should show more action. But none caught my fancy. Then diversifolius of botanically inclined recommended I follow the tree I said was my favorite: “a plants-and-rocks kind of tree, specifically a plant in rock.” Duh, of course I should! So what if it’s been dead for millions of years!
Sabalites powellii, a palm native to Wyoming (from the County Courthouse in Kemmerer; NPS).
Sabalites powellii is a kind of palm tree. It has no common name so I will call it “sabalites” (roughly saa-buh-LEE-tees   as if we knew how to pronounce Latin!). No one expects to find palms in Wyoming today, but fifty million years ago they grew in abundance on lake shores in the southwest part of the state. A beautiful fossilized sabalites frond stands in the hallway to the Geology Museum at the University of Wyoming.
Fossil Lake was the smallest of the big Eocene lakes, but perhaps the richest in fossils.
Millions of fossils have been collected from the muck that accumulated at the bottom of Fossil Lake and turned to rock (now part of the Green River Formation). Most famous is our state fossil, Knightia—a fish closely related to herring. But there’s far more, e.g. stingrays, turtles, crocodiles, parrots, grouse, ants, bees, butterflies, dragonflies, mosquitos, spiders, snails, ferns, cattails and palm trees.
Fossilized Knightia, University of Wyoming Geology Museum.
Clawed bat (NPS).
The fossils of the Green River Formation are one Wyoming’s greatest resources, and yet all these years I’ve ignored them. It’s time to make amends! However a visit to Fossil Lake will have to wait, as the climate is no longer subtropical. Wyoming winters are no longer suitable for camping, hiking, and outdoor contemplation. So I’ll go in May. Until then, there’s plenty to learn about palm trees, the Green River Formation, the environment of southwest Wyoming 50 million years ago, and fossils in general. For example, how do paleobotanists get away with naming a new species based on such poor fragmentary specimens?! We caenobotanists** could never do that.
Designated type specimen for Sabalites powellii (then called Sabal Powellii), collected in the 1880s (source).

My fascination with the history of scientific exploration in the American West is another reason to follow this palm. Its discovery dates from the exciting era of the great post-Civil War geological and geographic surveys. The story includes characters like geologist Ferdinand Vandeveer Hayden, infamous for self-promotion but also an effective advocate, and paleobotanist Léo Lesquereux, a most amazing adventurer who started when he was 65 and completely deaf. Now there’s a role model!
Paleobotanist Léo Lesquereux. In 1870, he joined Hayden’s expedition to the western territories (source).
“I have lived with nature, the rocks, the trees, the flowers. They know me, I know them. All outside are dead to me.” –Léo Lesquereux


The beginning of the year is a perfect time to join us in tree-following. It’s easy, requires only as much time as you wish to give, and is always interesting. For more info, click on the links at the top of the post.


** I made up caenobotanist as I needed an antonym to paleobotanist (old botanist); caeno is Greek for new.

Tuesday, January 3, 2017

More Story-telling Rocks

Curiously-arranged stones say it used to be much colder, and not that long ago.

Laramie winters are cold, with daily highs generally below freezing. Winds blow hard, often 30 to 40 mph, gusting to 50, 60, even 70. When arctic air masses visit, temps drop well below zero (F) and we post numbers and pictures on Facebook to show what we have to endure. But we shouldn't brag. Our local rocks and dirt tell us that Laramie weather could be much worse.

Twelve thousand years ago—a mere blink of a geologic eye—an ice sheet covered North America as far south as today’s central Montana, North Dakota, and eastern South Dakota. It never reached Wyoming, but we weren’t exempt from the bitter cold. Most of our basins contained permafrost, with only the uppermost soil melting in summer. When it refroze, expansion cracked the surface, year after year, creating networks of polygons. Now they’re buried under soil, except where fortuitously revealed by disturbance.
Relic frost polygons exposed during road construction at Crescent Junction, Wyoming (Mears 1987).
Frost wedges (polygons in cross-section) at the Rawlins city dump (Mears 1987; arrows added).

In the mountains, it was cold enough that snow survived summer melting. It accumulated, turned to ice, and began to flow, as glaciers. In the Medicine Bow Mountains west of Laramie, alpine glaciers merged into an ice cap across most of the crest, except for the highest part—the Snowy Range, a long steep-sided ridge of hard quartzite. Glaciers scratched and polished the rock only at the base; snow and ice didn’t accumulate above, at least not enough to form glaciers.
The Snowy Range stood above the alpine ice cap (SH Knight 1990).
Field assistant cavorts on the gently-rolling crest of the Medicine Bows; Snowy Range behind.
Though unglaciated, the Snowy Range was not immune to cold. Frigid conditions left their mark in other ways, most obviously the abundant felsenmeer (rock seas)—massive accumulations of boulders created by water! Bit by bit, expansion with freezing shattered solid quartzite into huge jumbled piles of angular blocks.

The trail to the summit of Medicine Bow Peak repeatedly crosses felsenmeer, fortunately via paths built by trail crews. The summit itself is a giant rockpile.
My old pal Sparky takes a break en route to Medicine Bow Peak.
Final section of trail to the summit. See any patterns in the plants and rocks in the foreground?
Emmie summits Medicine Bow Peak, her first ascent.

Just before the final push to the summit, the trail crosses a saddle underlain by a basalt dike (older sources call it diorite). Basalt is softer than quartzite and weathers more easily, explaining the low area with soil. Short alpine plants form turf among lichen-covered rocks—a meadow of sorts.
View of meadow from summit trail, in late August.
Meadow on basalt dike; older sources call it diorite.
Dike from below, near Sugarloaf trailhead.
From the right perspective, one sees that rocks in the little meadow are not randomly scattered. They outline polygonal patches of vegetation. Sound familiar? Yes, these are permafrost features—stone nets. Rocks and dirt were sorted, by annual freeze-thaw. Currently, active stone nets are common in Alaska, northern Canada, and other places with permafrost.
Above, stone nets seen from the trail to Medicine Bow Peak, looking south (Mears 1962). Below, roughly the same view in 2016; the nets are much harder to see. The illustrator emphasized rocks over plants, for clarity.
In the early 1960s, researchers dug a trench to study structural details. Larger rocks had accumulated along the sides of the polygons, with slabby ones often oriented on-edge. A dark (organic) layer of soil supported vegetation; plant roots extended as deep as three feet. When the study was over, they refilled the trench.
These stone nets are easiest to see from the ground, looking west slightly downhill (e.g. photos below). On gentle slopes, rocks have been sorted into lines that anastomosed into polygons. On steeper areas they form stripes.
As far as I could tell, common plants included alpine avens, moss campion, short sedges and a nearly-prostrate alpine willow. I need to return when things are blooming!
At the time of Mears’s 1962 publication, no one understood the mechanism behind frost sorting. Since then, computer modeling has suggested that with severe freezing, wet rocky soil expands enough to lift larger rocks and push them aside. Finer materials remain because they flow in response to frost heaving (more details here).
Sorted rocks are covered in lichen, suggesting they haven’t moved in awhile.
Developed soil, vegetation, long plant roots, and lichen-covered rocks indicate these stone nets are no longer active. But that could change. If another glacial episode were to override our global warming, stone nets and frost wedges would grow again. And here in Laramie, it may not have to be all that much colder!
Blizzards often close I-80, filling Laramie with trucks. Would life go on if glacial times returned?

• • •

Thirty-three years have passed since we lined up along a ditch to admire relic frost wedges, but the memory is still vivid. It was early October and snowing Laramie snow—horizontal with the wind. Doc Mears spoke of Pleistocene times 12,000 years ago, his strong baritone easily penetrating the howling wind, while we took notes as best we could with wet cold shivering hands. “I estimate the average annual temperature need drop just 10º C for a return to full periglacial conditions,” intoned Mears. None of us doubted it!
Dr. Brainerd “Nip” Mears, Jr. at Hanna Junction, 1970. Mears’s discovery of relic ice wedges was a major contribution to our understanding of Wyoming paleoenvironments. Photo by Wayne Sutherland.

Sources (in addition to links in post)

Knight, SH. 1990. Illustrated geologic history of the Medicine Bow Mountains and adjacent areas, Wyoming. Geological Survey of Wyoming Memoir 4. PDF

Mears, B, Jr. 1962. Stone nets on Medicine Bow Peak, Wyoming. Short note, University of Wyoming Contributions to Geology (p. 48).

Mears, B, Jr. 1987. Late Pleistocene periglacial wedge sites in Wyoming: an illustrated compendium. Geological Survey of Wyoming Memoir No. 3. PDF

Mears, B, Jr. 2001. Glacial records in the Medicine Bow Mountains and Sierra Madre of southern Wyoming and adjacent Colorado, with a traveler's guide to their sites. Geological Survey of Wyoming Publ. Info. Circ. No. 41. PDF

Thursday, December 29, 2016

2017 Wishes, Plans and a Resolution

Life ahead.
First …

Best wishes to all!! May your 2017 be filled with plants, rocks and good times. And fellow bloggers—please keep blogging! I would miss you if you quit.


Plans

Travel in a new-to-me field vehicle thanks to the uninsured driver who totaled my Honda CRV just before Christmas. No injuries, not much expense (thanks, Geico) and a low-mileage replacement CRV that doesn’t look like a baked potato.
Field vehicle and field assistant then …
… and now.


For tree-following, track an extinct palm tree, including a visit to its home on the shores of tropical Fossil Lake in southwest Wyoming (fertile imagination required).
Southwest Wyoming 50 million years ago (Chicago Field Museum).

Pursue life-long learning (antidote to aging says Mike the rock guy), specifically Basin and Range Volcanism at the University of Wyoming. Classes are free now that I’m 65! Expect volcanic posts.
Lunar Crater volcanic field in central Nevada.

Make a pilgrimage to the Central Coast of California in search of ophiolites, wildflowers, and lost youth.
Youthful days on the Coast of Dreams.

Return to South Pass (southern Wind River Range) in search of more rare rockcresses.
I will carefully search among Captain JC Fremont's "irregular lumps of clay."

And then—who knows? But I’m prepared, as this year I have a resolution: Always keep eyes, ears and mind open to new opportunities and adventures.

Still round the corner there may wait
A new road or a secret gate,
And though I oft have passed them by,
A day will come at last when I
Shall take the hidden paths that run
West of the Moon, East of the Sun.

Once I met a crystal unicornat Cottonwood Falls. Who would have guessed?!!

Monday, December 19, 2016

What are these rocks telling us?

“The heart of field geology is going up to rocks and getting them to tell you their stories” (source).
Beneath us are hundreds of feet of rock, often in layers that can be read like chapters in a book … if only we could see them! Fortunately, rivers sometimes come to our aid, cutting down through rocks to reveal their stories. Probably the most famous is the masterpiece cut by the Colorado River—the Grand Canyon. This is a story 1.75 billion years long, told in a stack of rocks a mile thick. The tale is fairly straightforward; sediments were turned to rock but otherwise not much altered. They remain mostly flat, like an immense layer cake.
Panorama from Point Sublime. WH Holmes, 1882. David Rumsey Map Collection.

But sometimes the reading isn’t so easy. Consider the cuts made by the Yampa and the Green, near their confluence on the south flank of the Uinta Mountains. I spent a long time pondering them, and never really understood the whole story. But I didn’t mind—it was a beautiful and remarkable place to be.
“Like an expression of frozen movement, or of time standing still, these faults accent the grandeur of the scene and stir wonder in the heart of the viewer.” Wallace Hansen, 1969
Confluence of Yampa and Green Rivers. View from Harpers Corner Trail, Dinosaur National Monument.
First I had to figure out which river was which. Fortunately I had help—the Harpers Corner Trail Guide (river labels circled: yellow – Yampa, green – Green).
The Green River flows south behind a long sandstone fin, is joined by the Yampa, and then turns back sharply to the north. In the photo below, the dashed arrow is the Green behind the long sandstone fin.
A Google Earth view helps:
These are crazy rivers!
The Yampa and the Green are thought to be superimposed drainages. There was a time when the Uinta Mountains were nearly buried in their own debris—sediments eroded off the range—and the Yampa and the Green flowed across the thick layer of debris as broad meandering streams. But then the region was uplifted, and erosion exhumed the buried mountains. The meandering rivers were “lowered” onto the underlying rocks, but they kept cutting down and maintained their circuitous paths! The Yampa is especially sinuous, winding for 22 miles through narrow canyons to cover less than ten air miles before joining the Green. [The whole story is more complicated; see Hansen 1986).]
Looking east up the Yampa River, above the confluence with the Green.
After making the sharp bend back north, the Green heads west and crosses the Mitten Park Fault, which it has exposed spectacularly for all to enjoy.
“Few faults anywhere are better displayed” (Hansen 1969). USGS photo, 1959.
These rocks started as sediments laid down on beaches, shallow sea floors, and in deltas and swamps, layer after layer. Next came humongous fields of sand dunes, and so on … for millions of years. The sediments were lithified, becoming a stack of mostly flat rock layers.

So why are they no longer flat? In fact, why are these rocks so severely deformed?! It's because they got caught up in mountain-building—specifically uplift of the Uinta Mountains between 70 and 40 million years ago.
Mitten Park Fault, NPS photo.
The folded rocks and fault were clear, especially with the trail guide to help, but the story behind them was not. This is not an easy read! The steeply-tilted rocks may be part of the local monocline—the huge step-like fold visible to the east. It’s broken by the Mitten Park Fault, with rocks to the east down-dropped relative to those to the west. Perhaps they were drug along the fault as the blocks moved past each other, creating the spectacular folds or enhancing those already there.
Monocline arrow marks change in dip from steep to gently-sloping.
Rocks left (west) of the fault are older and still roughly horizontal. Those at the same level to the right (east) are younger and severely deformed.
The timing is unclear. Some sources suggest the Mitten Park Fault came to be during the main uplift of the Uinta Mountains. Or it may represent a later stage, when the crest of the eastern Uintas collapsed (wow!). Movement may continue into the present.

In any case, these folded faulted rocks lay deep underground until the Green and Yampa Rivers finally cut down far enough to expose them.

Contrary to appearances, it wasn't a cataclysm that produced these tortuous rocks—just slow steady work. Crustal plates shifted a bit, rocks gradually folded, fractures grew inch by inch, maybe there was an occasional earthquake. This went on for tens of millions of years. Then the rivers went to work, slowly excavating dirt and debris, eventually exposing the rocks. But even with a plot this monotonous, a story tens of millions of years long can have a dramatic climax.
Having added a tiny bit of dirt from Mitten Park to its load, the Green continues on (NPS).

This is the last post from my September trip to the Uinta Mountains—a place I had long wanted to visit (~30 years) and finally did. Two weeks were only enough for an introduction; I need to return. Many thanks to Mike of CSMS GEOLOGY POST for the encouragement, and for recommending books to read, places to go, things to see.


Sources

Frishman, JA. 2011. Crest, Cliff and Canyon (blog), Geology of Dinosaur National Monument.

Gregson, JD, and Chure, DJ. 2000. Geology and paleontology of Dinosaur National Monument, Utah-Colorado: in Sprinkel, DA, Chidsey, TC, Jr. and Anderson, PB, eds. Geology of Utah’s Parks and Monuments. Salt Lake City: UGA Publication 28, p.155-188.

Hansen, W. 1969. The geologic story of the Uinta Mountains. USGS Bulletin 1291. PDF

Hansen, W. 1986. Neogene tectonics and geomorphology of the eastern Uinta Mountains in Utah, Colorado, and Wyoming: USGS Professional Paper 1356.

Untermann, GE, and Untermann, BR. 1969. Popular guide to the geology of Dinosaur National Monument. Dinosaur Nature Association. (out of print)