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.

Great Skyroad Opens Wonderland to Public Travel

Cars on Libby Flats at the base of the Snowy Range, southeast Wyoming; July 4, 1926; courtesy American Heritage Center, University of Wyoming.

This article will appear in Sunday's Laramie Boomerang, our daily newspaper,  founded in 1881 by Bill Nye. He named it after his mule “who always came back.” I contribute to the popular “Laramie’s Living History” column, usually writing about botanical and geological features. But this is all human history, with the exception of some “glacial ice.”

Celebrating the “Great Skyroad”

On the morning of July 4, 1926, it was raining hard. But that didn’t stop the watermelon crew. They left Laramie early, reaching the summit well in advance of the ceremonies. There they buried two tons of melons in snow. Unfortunately, by mid-day the new road was thoroughly soaked, and struggling automobiles had churned it into an unnerving muddy mess. Many turned back. The Governor arrived two hours late.

Yet the ceremony went largely as planned, with hundreds of chilled but cheerful onlookers celebrating the opening of the Great Skyroad across the Snowy Range. Though the name didn’t stick, the road was a great success, opening areas previously inaccessible, and allowing for many activities across the range.

FIFTY YEARS OF IMPROVEMENTS
The first wagon roads into the high Medicine Bow Mountains appeared in the 1870s, built by loggers, miners, and tie hacks from the railroad. By the late 1890s a road of sorts extended across the range. But sections were quite rough, barely passable to wagons.

In 1909, the Forest Service, Albany County, and the town of Centennial contributed a total of $2500 for road improvements between Centennial and Brooklyn Lake. The first auto arrived at the lake a year later, a new Franklin driven by Forest Supervisor P.S. Lovejoy. The nine-mile trip (one-way) took an hour. Lovejoy must have been an adventurer and skilled driver, for the road to the lake was said to be impassable to autos, and would remain so for a decade.

[NOTE: This Lovejoy is not to be confused with Laramie’s inventor Elmer Lovejoy, of bicycle and automobile fame, and it’s unknown whether the two were even related. But Supervisor Lovejoy may well have bought the Franklin he drove to Brooklyn Lake at Lovejoy Novelty Works, where Elmer sold both bicycles and automobiles. P.S. Lovejoy left Laramie around 1911, moving to Ann Arbor to teach in the Forestry program at the University of Michigan.]

Elmer Lovejoy’s Garage and Service Station c. 1920; courtesy Laramie Plains Museum.

In 1920, the federal Office of Public Roads and Rural Engineering (today’s Federal Highway Administration) provided Wyoming with $25,000 to improve the road to Brooklyn Lake, which had become popular with local recreationists and, increasingly, tourists. Those sections not covered by the feds were upgraded by Albany County.

The obvious next project began in 1924—a road passable to autos across the high Medicine Bow Mountains. Fully funded by the federal government, it would continue 22.5 miles west from the Brooklyn Lake road to the Forest boundary, where it would join with an existing road from Saratoga. The roadway would be ten feet wide with a surface of graded dirt (graveling and then paving of the Snowy Range Road didn’t start until the 1930s).

BIGGEST PICNIC EVER

By the summer of 1926, the road over the Medicine Bow Mountains was essentially in place. A dedication ceremony was in order, and what better day to celebrate than July 4, our nation’s birthday. A committee was formed, and plans were made. On July 3, the Laramie Republican-Boomerang announced that the dedication exercises, which would start at noon, would be followed by “the biggest picnic ever held in the state.” Watermelons chilled in “glacial ice” and hot coffee would be provided. Attendees were to bring their own lunches.

But first the road had to be cleared of snow on both sides of the summit—not surprising given the earliness of the season. A call for volunteers went out. The Wyoming Reporter, a Rawlins paper, assured readers that a crew of 30 had successfully cleared the route with picks and shovels, though in places autos would have to pass between snow banks 10 to 15 feet high. Saratoga and Centennial supplied most of the volunteers, along with a few from the University (including President A.G. Crane). Notably, even though a “large number of people from Laramie were in the Snowy Range region … few volunteered to help open the road.”

On July 1, special traffic regulations for the day of the celebration were announced in the Laramie Republican-Boomerang: “Forest and sheriff’s officers will be stationed at key points along the highway, and between the hours of 10 and 12, only ‘up’ traffic will be permitted. Between 12 and 2 will be reserved for ‘down’ traffic and the hour between 3 and 4, if necessary for ‘up’ traffic. A speed limit of fifteen miles per hour will be in effect on all sections of the road where the need warrants.” As it turned out, 15 mph was overly optimistic.

BRAVE DRIVERS REAP REWARDS

July 4 dawned rainy, with especially heavy downpours on the east side of the range. This “greatly hindered the progress of the multitude of automobiles that had come for the exercises” according to the Laramie Republican-Boomerang. The wheels of hundreds of cars soon made the road slick and dangerous. Many turned back, especially those from Laramie and Cheyenne, the road up the east side being particularly treacherous.

However state officials led by Governor Nellie Tayloe Ross, along with representatives of the Forest Service and dignitaries from Rawlins, Laramie, Cheyenne, Parco, Saratoga and Encampment, braved the conditions and reached the summit, though two hours late. But that was just as well, as the skies had cleared only an hour before.

There they found either 400-500 (Rawlins Republican) or 600-700 (Saratoga Sun) participants in a celebratory mood. A huge fire roared nearby, and, at the encouragement of President Crane, people were loudly singing “It Ain’t Gonna Rain No More …”

A speaker’s platform had been assembled from two table tops, laid across the sides of a truck. Here the most important dignitaries sat while Governor Ross dedicated the “Great Skyroad” (see photo). The Laramie Republican-Boomerang would report the following week that “Governor Ross made a particularly fine appearance that morning, standing up there on the roughly improvised platform, and her voice which is especially clear and pleasing, seemed to reach even the outer edges of the crowd, who paid their marked attention.”

Warmed by a roaring fire, Governor Nellie Tayloe Ross (standing on platform) dedicates the "Great Skyroad" over the Snowy Range; July 4, 1926; courtesy American Heritage Center, University of Wyoming.

According to the Boomerang, ceremonies were carried out as planned “with some necessary omissions.” Hundreds of chilled watermelons were enthusiastically consumed. However, the Rawlins Republican reported that participants from the west side of the range were “sadly disappointed” when the promised hot coffee was nowhere to be seen on Libby Flats. Instead, it was available 15 miles down the road toward Laramie, where lunch for the official party was being served. Given the slippery roads, a 30-mile side trip did not appeal to those returning home to the Platte Valley. “Why the coffee was not served at the point where the exercises were held is a mystery.”

The following week, local papers were in general agreement that the ceremonies and especially the new road were a great success. The Boomerang argued that given the morning’s storm, “it would not be fair to judge the road by its condition on Sunday … any road having something like half a thousand cars churning over it both coming and going is bound to manifest the effects.” Those who reached the summit and even those who made it just partway “were enthusiastic with what they saw, the wonderful vistas of mountains in the distance and the plains stretching beyond the almost countless lakes and ponds of beauty and the rushing, tumbling streams.”

The Saratoga Sun was equally effusive but more succinct: “In spite of the discomfort occasioned by the downpour of rain, however, all were agreed that the new highway has opened to public travel a wonderful scenic region, which will no doubt prove to be a favorite resort for outers and vacationists during this and succeeding summer seasons.” So true!

[by Hollis Marriott, Contributing History Columnist; Laramie Boomerang, August 18, 2019]

Sources

Wyoming Highway Department & Federal Highway Administration. 1988. Dedication ceremony; New Wyo 130 (Snowy Range Road). 12 pp.

Wyoming Newspapers. Online database. https://newspapers.wyo.gov/ (accessed August 2019).

Beach-combing 11,000 Feet above Sea Level

My old friend Sparky, on an early Proterozoic beach in southeast Wyoming.

West of Laramie, Highway 130 crosses the rolling grasslands of the valley bottom for about 30 miles and then begins to climb, winding up through the Medicine Bow Mountains, through conifer forest and quaking aspen, past meadows and small lakes, past streams lined with yellow, blue and red wildflowers. Polished boulders lie scattered about, sparkling in the sun. For ten miles the road climbs. The meadows get bigger, the trees smaller. There are more and more boulders and outcrops until finally the landscape is dominated by rock. Most prominent is the Snowy Range—a wall 1500 feet high and seven miles long—a beach turned on its side—5600 feet of sand transformed into rock.

In 2014, the US Forest Service installed geological interpretive signs, designed by the Wyoming Geological Survey, at the high point of Highway 130. No longer are we limited to today’s scenery. Now we can view the Snowy Range in deep time—two billion years ago!—and appreciate the Earth’s awesome powers.

Accumulation

If we were to travel in time as well as space, and visit southeast Wyoming two billion years ago (early Proterozoic time), we would be standing on the southeast coast of a young North America. Looking northeast, we would see mountains in the distance. Erosion was rapidly wearing them down, being unimpeded by vegetation (land plants wouldn’t appear for another 1.5 billion years). Streams carried massive amounts of debris to the coast where they dropped their loads, building deltas and beaches.

Of course this tranquil coastal scene was not to last, the Earth being what it is—dynamic.

Transformation

A few hundred million years later, a drifting continental fragment or several island arcs bumped up against the coast. A collision of this scale has serious repercussions. The beds of sand—by now lithified into sandstone—were deformed into large steep folds. Immense pressure and heat transformed the sand to very durable quartzite. The landscape must have been spectacular, maybe similar to the Himalayas or Andes. But it too was ephemeral and soon gone—worn down and buried under younger sediments. The quartzite would lie hidden from view for something like 1.5 billion years.

Revelation

Then once again the land was shoved up and folded, during the widespread deformation that created the Rocky Mountains 70 to 40 million years ago. Erosion went to work immediately, as it does whenever mountains are uplifted, and the younger sedimentary strata were worn away to reveal rocks that came to be two billion years ago along that ancient coast. So let’s go beach-combing!

Emmie is fascinated by early Proterozoic rocks.

We won’t find any shells or seaweed or dead fish on this beach—two billion years ago was much too early for complex life—but our beach-combing will still be productive. Even though the quartzite is quite ancient, the metamorphism was low-grade (“only” 200-300º C), so structures and features of the original sand deposits are still visible! These are some of the clues geologists use to reconstruct the environment here two billion years ago (of course they don’t always agree).

The Snowy Range is mostly Medicine Peak quartzite, which is highly resistant to erosion. That’s why the Range stands above the rest of the Medicine Bow Mountains.

Original beds (layers) are still visible (left of center, beyond lake; click on image for a better view).

On the west side of Mirror Lake, beds of sand-turned-to-rock are tilted to nearly vertical.

Fine-scale sedimentary structures are common—such as bedding, cross-bedding, and layers of pebbles. Various minerals add color. Much of the rock is polished, for as recently as 12,000 years ago, glaciers were grinding their way across this area. Beauty combined with views into an ancient world keep me looking at rock after rock after rock.

Often the quartzite appears striped—showing layers of sand deposited at different times, under different conditions, or maybe from a different source.

Cross-bedding is common in places. The scale of the beds indicates this sand was deposited by water, perhaps in a river or subtidal delta (vs. large scale cross-bedding created by wind, as in dunes).

Medicine Peak quartzite includes occasional layers of quartz pebbles, sometimes enough to qualify as quartz pebble conglomerate. Pebbles need more vigorous transport than sand; maybe they were deposited when streamflow was high.

Arrows point to a pebble layer in cross section.

Closer view.

See that dark one?

It’s quartz pebble conglomerate!

An even better one!! It's so hard to quit searching ... just like in beach-combing.

The Snowy Range is about 45 miles west of Laramie, via Wyoming Highway 130. Stop at Libby Flats and the overlook to the west for great views, invigorating mountain air, and a healthy dose of geological edification.

(10,847 feet above sea level)

Snowy Range in the Medicine Bow Mountains. Arrow marks pullouts with geological signs (Google Earth).

Sources (in addition to links in post)

Hausel, WD. 1993. Guide to the geology, mining districts, and ghost towns of the Medicine Bow Mountains and Snowy Range Scenic Byway. Wyoming State Geological Survey Public Information Circular No. 32.

Houston, RS, and Karlstrom, KE. 1992. Geologic map of Precambrian metasedimentary rocks of the Medicine Bow Mountains, Albany and Carbon counties, Wyoming. USGS Miscellaneous Investigations Series Map I-2280. PDF

Karlstrom, KE, and Houston, RS. 1984. The Cheyenne Belt; analysis of a Proterozoic suture in southern Wyoming. Precambrian Research 25:415-446.

Lanthier, LR, 1979. Stratigraphy and structure of the lower part of the Precambrian Libby Creek Group, central Medicine Bow Mountains, Wyoming. Contributions to Geology, University of Wyoming. 17:135-147. 

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. Wyoming State Geological Survey Public Information Circular No. 41.