The Snowy Range, 2 billion years in the making

Medicine Bow Mountains and the Snowy Range rise above the Laramie Plains.

In the early 1980s, author John McPhee was gathering information for a book, Rising from the Plains, about Wyoming geology. He crossed the state on Interstate 80 from east to west, in the company of one of the grand old men of Wyoming geology, the late John David Love. McPhee took notes while Love drove and expounded on the landscape.

Near Laramie, as they looked west at distant mountains, McPhee was struck by the illusion: "... the Medicine Bow Mountains and the Snowy Range stood high, sharp, and clear, each so unlike the other that they gave the impression of actually being two ranges ... the flat-crested Medicine Bows, dark with balsam [subalpine fir], spruce, and pine; and, in the far high background, the white and treeless Snowy Range."

In fact, the latter sits atop the former, and geologically they are one.

Ancient sediments

In 1868, just a few months after Laramie was established, Arnold Hague of Clarence King's Fortieth Parallel Survey became the first geologist to explore the Medicine Bows. In his 1877 report, Hague described a flat-crested mountain range with "elevated plateau country, nearly 10,000 feet above sea-level ... dotted over with numerous alpine lakes." From this high surface rose a sharp-edged ridge that "culminates in Medicine Peak, a grand, broad central mass." [The plateau country is now Libby Flats, the ridge the Snowy Range, and the high point Medicine Bow Peak.]

The Snowy Range on the horizon, above Libby Flats.

"... the amphitheatres, with mural faces 1,500 feet deep, cut out of pure white quartzite, are very striking," wrote Hague. The peak itself "is a mass of pure white quartzite, rising nearly 2,000 feet above the surrounding country ..." He assigned the quartzite to what was then called the "Archean series"—the oldest rocks on Earth, specific age unknown. At that time, it was the best a geologist could do.

Hague found layers of pebbles and other signs of bedding in the quartzite, convincing him it had started as deposited sediments. He also concluded that the beds, originally horizontal, had been steeply tilted. But if he had further thoughts about how the quartzite and ridge formed, he didn't share them.

Pebbles in quartzite, cited by Hague as evidence of sedimentary origins.

Two decades later, a geology graduate student from the University of Wisconsin, Charles Van Hise, crossed the Medicine Bow Mountains on horseback in just three days. During his brief visit, he examined the rocks at the crest, taking notes for his PhD dissertation about North America's Precambrian rocks (equivalent to "Archean series" used by Hague). Like Hague, he described the quartzite as ancient and sedimentary.

Neglected no longer

In 1917, a third geologist came to southeast Wyoming to study the Medicine Bow Mountains. "Dr. Eliot Blackwelder, head of the department of geology at the University of Illinois arrived in this city this morning ..." reported the Laramie Boomerang on July 24. He would "start on a geological expedition in the Medicine Bow mountains in a few days." Blackwelder was interested specifically in the ancient rocks at the crest.

Blackwelder found the Medicine Bows a wonderful place to work, as he explained in his report. "In spite of its ready accessibility, this interesting range has been strangely neglected by geologists until the last decade. ... no detailed work seems to have been attempted." He would fill that gap, spending six weeks in the range in 1917, and a month in 1925.

At the end of 1926, Blackwelder published his Precambrian geology of the Medicine Bow Mountains. He named the "great, massive quartzite" of the Snowy Range the Medicine Peak quartzite, describing it as "extraordinarily thick"—on the order of 5600 ft! He too concluded it consisted of metamorphosed sediments dating from Precambrian time (but still without a specific age). Unlike his predecessors, however, Blackwelder offered a probable scenario for its origins.

Cross-section through the Medicine Bow Mountains in the area of the Snowy Range. Note the thickness of the Medicine Peak quartzite! (labeled "D"). Blackwelder 1926.

 Medicine Peak quartzite above Mirror Lake. Added arrow points to a huge dike—magma injected into the quartzite. Blackwelder 1926.

Reading the rocks

The Medicine Peak quartzite started as quartz sand, became sandstone, and then was metamorphosed under intense pressure to its final form—very hard rock that sparkles in the sun. Yet it still provides clues about its ancient birth. Blackwelder often spotted ripple marks and cross-bedding (layers at angles), evidence that the sand had accumulated in shallow active water. He suggested it was deposited just offshore, where it would be shaped by waves, or streams flowing into the sea.

Cross-bedding preserved in Medicine Peak quartzite; block is about 1 m long.

And yet the quartzite was so thick—at least 5600 ft even after compaction and metamorphism! How could so much sand accumulate in shallow water? Blackwelder turned to a modern-day analogy. "The great thickness of pure quartzite represents sifted sand that might have been deposited and worked over on a marine shelf, like that around Cape Hatteras, on the Atlantic coast of the United States."

But if so, how did sand on a marine shelf become quartzite 11,000 ft above sea level, far from any ocean? In Blackwelder's day, there was no good answer for this kind of question. It would be almost 40 years before enlightenment arrived.

Earth's dancing plates

By the early 1960s, geologists had accumulated enough evidence to put forward the theory of plate tectonics, now widely accepted. The Earth's rigid outer shell, the lithosphere (crust and upper mantle), consists of giant "tectonic plates" that grow, break, stretch, compress, dive under, thrust over, and collide in a slow but powerful dance. In the process, landscapes are changed on a grand scale.

Earth's plates (source)—very different from 2 billion years ago.

It was the movement of tectonic plates that created the Snowy Range. Here's the basic plot: Along the Wyoming coast, a massive amount of sand accumulated offshore. A plate collision pushed up mountains, metamorphosing and tilting the sand(stone). These mountains were worn down, their remnants buried. Then another tectonic confrontation pushed up the Medicine Bow Mountains. Erosion exposed the ancient quartzite and shaped the Snowy Range.

The former world

The Medicine Peak quartzite started as sand 2.1 billion years ago. Back then, Wyoming was part of Superia, a smallish supercontinent. But Superia was coming apart, leaving Wyoming on the coast of a growing ocean. Sand and other sediments would accumulate just offshore for some 200+ million years.

Modified from Mitchell and others, 2021.

Then something changed, something huge! Exactly what may be lost to deep history, or maybe not yet discovered. In any case, the widening ocean disappeared.

Collision and a continental suture

In their studies of the quartzite, Hague, Van Hise, and Blackwelder all could see that the beds of sand, which were horizontal when deposited, were now far from it. "In general the sedimentary beds are nearly vertical or steeply inclined to the southeast," wrote Blackwelder. They had been tilted almost 90 degrees!

The cause was continental collision. About 1.78 billion years ago, a smallish tectonic plate called the Green Mountain Terrane bumped up against the Wyoming coast. This "collision" went on for 40 million years, producing among other things a continental suture called the Cheyenne Belt—a zone of highly deformed rocks.

Inferred location of the Cheyenne Belt, a continental suture (original source unknown).

Deformed rock of the Cheyenne Belt, Medicine Bow Mountains (field trip stop 1); ruler is 15 cm.

As is typical for such a collision, a mountain range was pushed up, tilting the sand-turned-to-quartzite on its side. But that mountain range is now mostly gone. Though they may seem permanent to us, mountains too have lifetimes. As soon as they rise, erosion goes to work wearing them down, sometimes burying them in their own debris.

The remnants of the ancient range would lie buried for hundreds of millions of years, while sediments accumulated to great thickness. The quartzite would be covered by tens of thousands of feet of limestone, sandstone, and shale by the time the next big change arrived.

West Coast happenings impact Wyoming

That change was uplift of the Medicine Bow Mountains. It happened during a great mountain building event called the Laramide Orogeny, which started 80 million years ago, lasted almost 40 million years, and created mountain ranges from Mexico to Canada—the Rockies. In contrast with the previous collision, the plate jostling this time was remote. Almost a thousand miles to the west, the oceanic Farallon plate was diving under the North American plate, compressing the continent and pushing up mountains far inland.

Rocky Mountains due to subduction far to the west (source). 

Of course, as soon as the Medicine Bow Mountains rose, erosion set in. Eventually enough of the sedimentary rock cover was removed to expose the ancient Precambrian core. Being super hard and durable, the Medicine Peak quartzite eroded much more slowly, and was left as a high-standing ridge.

As Eliot Blackwelder would write 40 or 50 million years later, "The Snowy Range owes its prominence and position to a great, massive quartzite formation."

Field trip—you too can read the rocks!

The Snowy Range at the crest of the Medicine Bow Mountains, just 50 miles west of Laramie.

This tour includes five stops—four at the crest and one en route. Start early to include a hike to the summit of Medicine Bow Peak.

Zero your odometer at the junction of Highways 130 and 230 in West Laramie, and drive west on 130. At about 19.5 miles, as you descend into the Centennial Valley, slow down to take in the view. Immediately ahead are the forested Medicine Bow Mountains. Seemingly behind and above is the Snowy Range. Even this close, the illusion persists.

1. At 36 miles, turn right and park along the Brooklyn Lake Road near Nash Fork Campground. To view a bit of the 1.78 billion year old continental suture, walk into the campground, stay left on the loop, and just past the fee station and site 27, walk left (west) 20 or 30 yards to dark rock above the highway. Look around your feet for fine laminations, with waves and tight chevrons created by continental collision. Then check the two huge white quartzite boulders (dropped here by glaciers) for cross-bedding from deposition offshore, and gray bands with white pebbles flattened during collision.

2. At 40 miles, visit Libby Flats observation point (with restrooms and a "castle"). Enjoy Arnold Hague's "elevated plateau country ... dotted over with numerous alpine lakes."

3. A quarter mile farther west on Hwy 130, turn left to Medicine Bow Peak Over Look, with helpful interpretive signs. On the Snowy Range diagram, find The Diamond with Mirror Lake below—location of Blackwelder's photo included here, and the next stop.

4. Continue west 1.3 mile to Mirror Lake Picnic Area. Near the entrance, compare your view with Blackwelder's photo. In looking at the spectacular face, remember ... it is beds of sand turned vertical! From the high point of the loop, examine the large dark dike (marked in photo)—magma injected into the quartzite while it was still underground.

5. Continue west a short distance to the first of two Lake Marie parking lots. At the east end, explore the field of white quartzite boulders. Bedding and cross-bedding are common. Search to find gray bands with flattened white pebbles, evidence of plate tectonics in action!

A short distance farther on the highway is the west Lake Marie parking lot and a trailhead for Medicine Bow Peak, 12,013 ft elevation. The round trip is 8 or 9 miles. A shorter trail leaves from Lewis Lake, but doesn't have as much wonderful scenery in my opinion. A loop can be done to include both (see maps online).

Cross-bedded quartzite en route to Medicine Bow Peak from west Lake Marie trailhead.

Summit of Medicine Bow Peak—a giant pile of quartzite boulders.

Sources

Blackwelder, E. 1926. Precambrian geology of the Medicine Bow Mountains. Bull. Geol. Soc. Am. 37:615–658.

Hague, A. 1877. Medicine Bow Range, in US Geological Exploration of the 40th Parallel, vol. ii: 94–111. Washington, DC: GPO.

Hausel, WD. 1993. Guide to the geology, mining districts, and ghost towns of the Medicine Bow Mountains and Snowy Range Scenic Byway. WSGS Public Information Circular 32. Free PDF.

Sullivan, WA, and Beane, RJ. 2013. A new view of an old suture zone: evidence for sinistral transpression in the Cheyenne belt. GSA Bull. 125:1319–1337.

This post is based on my recent contribution to the History column of the Laramie Boomerang, which features articles by volunteers eager to share our local history. We also hope to relieve the dismal monotony of pandemic news, and support our flagging local newspaper! Articles are archived at the Albany County Historical Society website.

Frank Tweedy's Traveling Plants: WY to NYC & back

Frank Tweedy. Union College Special Collections (used with permission); date unknown.

Readers of this blog may remember Frank Tweedy of the US Geological Survey, who surveyed the Laramie Plains in 1892 (Mapping the Laramie Plains, 3rd dimension captured). In August of that year, the Laramie Boomerang announced that Tweedy and assistant James McFarland would "commence work upon the topography of this section of the country." Three years later, the "Laramie Sheet" was published—one of the first topographic maps for Wyoming.

In January of 1903, there again was a Frank Tweedy in the Laramie news. "Prof. Nelson [University of Wyoming] has received a rare collection of plants from Mr. Frank Tweedy ... a botanist of considerable distinction" reported the Republican. Were USGS surveyor Frank Tweedy and distinguished botanist Frank Tweedy one and the same? And how did 700 plants survive a trip to Laramie in January?!

Dead, flat, & dry

Actually, survival was not an issue, for these plants were already dead. But they still were of great value. All were collected in 1900 in the wilds of the northern Bighorn Mountains. There they were carefully arranged in paper folders so that parts needed for identification were visible, and placed in a plant press with absorbent felt sheets until dry (several days to several weeks, depending on weather).

After the field season, they made their way east, ending up at the New York Botanical Garden where the great botanist, Per Axel Rydberg, either identified them, or, if they were new to science, named them himself. Then in 1903, "upward of 700" traveled west to Laramie, each accompanied by a label with the plant's name, collection location, date, and collector—Frank Tweedy.

At the university there was more processing, for dried plants are fragile, and won't last long if left loose in paper folders. They were mounted on 11" x 18" sheets of durable paper, preserving them for centuries to come, and properly filed in the university herbarium.

Pleated gentian, Gentiana affinis, collected by Frank Tweedy in 1900. Rocky Mountain Herbarium.

Herbarium?

If you don't know what a herbarium is, you're not alone. Few people do. Many think it's some kind of greenhouse, but actually it's the opposite—a collection of pressed dried plants. The first, called a "hortus siccus" (dry garden), was created in the 1520s by Italian botany professor Luca Ghini. He wanted a way to teach plant identification in the winter, so he pressed and dried plants, and glued them to paper sheets. Fed up with their ancient textbooks, Ghini's students loved him for it.

Today, students still use herbarium specimens to learn to identify plants. But they took on a much bigger role during the golden era of global exploration (16th–19th centuries)—documentation of the world's flora. Herbaria proliferated and flourished. Now there are at least 3300, holding nearly 400 million pressed dried plants!

New herbarium grows fast

By 1892, the University of Wyoming had been operating for five years with a botany professor (Aven Nelson) but no herbarium! This was unacceptable for the state's only university. Fortunately, Experimental Station Supervisor Burt C. Buffum had collected Wyoming plants for several years, accumulating on the order of 500. Several hundred were set aside for an exhibit at the 1893 World's Columbian Exposition in Chicago. As for the rest, University President Albinus Johnson directed Nelson to use them to start a herbarium.

Nelson knew little about plant identification and herbarium management, but that didn't slow him down. In 1899, he launched an ambitious project. For 14 weeks, he traveled Yellowstone Park by horse-drawn wagon, with his wife, two daughters, and two students. They collected zealously, returning to Laramie with 30,000 specimens! Most were duplicates, to be sold or traded to fund and expand the UW herbarium.

Collecting plants in Yellowstone, 1899. Photo by Aven Nelson; American Heritage Center (AHC).

Before the trip, Nelson wrote to his esteemed colleague Per Axel Rydberg at the NY Botanical Garden, asking where in Yellowstone he should collect. Rydberg replied: "The flora of the park is, however, well worked up as several collectors have been in there ... The one that has done the most, however, is Frank Tweedy of US Geological Survey. He spent two whole summers in the park."

Indeed, surveyor Frank Tweedy and botanist Frank Tweedy were one and the same!

An eye for novelty

Frank Tweedy was born, raised, and educated in New York, graduating from Union College in 1875 with a degree in civil engineering. He began his surveying career the next year in the Adirondacks, followed by a stint as a sanitation engineer in Rhode Island. All the while, he collected plants.

If we follow Tweedy's trail of herbarium specimens (accessible online), we go from New York to New Jersey to Rhode Island. But then we make a huge leap west. In 1882, Tweedy went to work as a topographer on the Northern Transcontinental Survey in Washington Territory. And he collected plants.

For Tweedy, this was a very different kind of botanical world, largely unexplored and rich in novelties—species new to science. He collected his first that summer, a grass from the Wenatchee Mountains. It was named Tweedy's reedgrass (Calamagrostis tweedyi) by grass expert FL Scribner, who wrote: "Mr. Tweedy has been a careful and zealous collector of the plants of the various sections of our country which he has visited, and it is with pleasure that I dedicate this species to him."

Calamagrostis tweedyi, Tweedy's reedgrass, from American Grasses (FL Scribner 1897).

This was the first of more than 100 plant species discovered by Tweedy, and the first of at least 35 named in his honor. By the time his specimens arrived in Laramie in 1903, he was a highly-regarded pioneering botanist of the American West.

Erigeron tweedyi, Tweedy's fleabane. Photo by Matt Lavin (Flickr).

Herbarium in the news

Meanwhile the UW herbarium had grown rapidly, thanks to collecting by Nelson and his students, and acquisitions through purchase and trade. In 1899, he convinced the University Trustees to make it a separate institution—the Rocky Mountain Herbarium (as it is today), with Nelson as curator.

Within a few years, Nelson and the Rocky Mountain Herbarium had become newsworthy. In May of 1902, the Rawlins Republican reported "[a set] of 800 Wyoming plants has just been forwarded to the Carnegie museum (Pittsburg) by Professor Nelson" who also "received an interesting collection of plants, some 300 in number, from Dr. Riser of Rawlins ...". Even more notable, Nelson shipped a collection of potentillas (cinquefoils) to Germany, to "Dr. Theodore Wolf, a German botanist, who is preparing a monograph of all the species of the genus in the world." In exchange, German potentilla specimens would be sent to the Rocky Mountain Herbarium.

In July, the Cheyenne Daily Leader had exciting news. "12,000 Specimens of Rare Herbs and Plants for the State University" had been collected in Nevada, New Mexico, Utah, and Wyoming by Leslie Goodding, one of Nelson's students. About 800 species were represented, including every botanist's dream—species new to science (several were named in Goodding's honor).

University of Wyoming, 1901. AHC, SH Knight Collection.

According to the Laramie Boomerang, by September of 1902, UW's herbarium contained 36,000 specimens—impressive given there were still just three buildings on campus (not counting barns and greenhouses). At the end of the year, when Nelson's articles about saltbushes and hawthorns were published in the University of Chicago's Botanical Gazette, the Laramie Republican proudly and rightly declared, "Prof. Nelson is a recognized authority on Rocky Mountain and western plants."

Thus we shouldn't be surprised that a botanist of Tweedy's caliber would contribute a "rare collection of plants" to the Rocky Mountain Herbarium.

Imagining the past

During my research, I often imagined Tweedy and Nelson in conversation—the renowned western botanist encouraging Nelson's ambitions. Did they meet when Tweedy was surveying the Laramie Plains in 1892? Or maybe they made arrangements in May of 1901, when the Personals section of the Boomerang reported that "Frank Tweedy of Washington is in the city" (no further details).

I searched and searched for correspondence between the two men, eager to find a climax for this story. Instead, I discovered that the Republican, or perhaps Nelson, had led me astray.

In examining Tweedy's specimens at the Rocky Mountain Herbarium, I discovered a puzzling label on the lower left corner of each: "Received from A.A. Heller, 1903". As I would learn, Nelson didn't receive the specimens directly from Tweedy. He bought them from Amos Arthur Heller. (Heller probably got them through a trade, but we can't be sure.)

A fantastic bargain just the same

Heller was an American botanist active from 1892 to 1940. The standard botanical sources include his professorships in Minnesota, California, and Nevada, as well as work for prominent botanical institutions. But I knew nothing of his stint as a freelance plant dealer until I visited UW's American Heritage Center, where I found a folder of letters from Heller to Nelson. 

On December 3, 1902, Heller wrote Nelson from Puerto Rico: "If you care for them, I have a collection of 700 Wyoming plants collected by Frank Tweedy, which I will sell for $45.00. There are a lot of new species among them [named] by Rydberg, and I understand he [identified] the whole collection. I am giving you the first chance at these, as I know they will be of more value to you than any one else." He then advised, "If you want the Wyoming plants, Mrs. Heller [in Pennsylvania] will attend to sending them."

Apparently Nelson jumped at the opportunity. In a letter dated December 29, E. Gertrude Heller wrote: "I will ship you the plants at once ...", which she must have done since they arrived sometime before January 14, when their story appeared in the Laramie news.

Surely Nelson was happy with his purchase—nearly 700 specimens representing 500+ species, collected by a highly-respected botanist. And, as the Republican explained, "As not more than three of these sets of plants are in existence this herbarium is fortunate in securing one" (the others went to the National Herbarium and the NY Botanical Garden).

Furthermore, "since [Tweedy's] work carries him into many places, inaccessible to the ordinary collector, his plants are unusual and interesting." Here the Republican was correct. A dozen of the specimens were species new to science! Obviously Frank Tweedy was very good at spotting botanical novelties, even while surveying.

Tweedy's gilia (Gilia tweedyi), collected by Frank Tweedy in the Bighorn Mountains. Dried plant is about 8 in tall. H. Marriott photo; added flower photo by Matt Lavin, 2012 (Flickr).

🌺🌼🌾

This post is based a recent contribution to the History column of the Laramie Boomerang, which features articles by volunteers eager to share our local history. We also hope to relieve the dismal monotony of pandemic news, and support our flagging local newspaper! Articles are archived at the Albany County Historical Society website.

For more about Frank Tweedy, perhaps our most under-appreciated pioneering botanist, see his Wikipedia page. It was created just last year by this author (herself a botanist), and Noel Sherry, who is exploring Tweedy's mapping, plant collecting, and more.

Tree-following: Red and Green

Both trees I'm following this year are red and green, but in different ways. Last month, Flash the maple was covered in green leaves and red samaras. The samaras are still red but looking duller. And the leaves are starting to turn red. It hasn't been cold, not even close. Could this be due to heat and smoke? Or maybe just normal life for Flash.

Spike the hawthorn still has rich green leaves, while the young emerging leaves are reddish. No flowers or fruit this year, but that's fine. Having nearly died (or so it looked!), Spike is to be commended for the healthy shoots and foliage.

Fresh young hawthorn leaf, with ant.

This my contribution to the August gathering of tree-followers. Thanks to The Squirrrelbasket for hosting!