Mysterious Stones of the Laramie Mountains

A story of granite, grus, and tors.

If you wander the summit of the Laramie Mountains as dusk falls, chances are you will spot mysterious creatures silhouetted against the evening sky—giants forever waiting by their castles, life-like but never moving. But if you get too close, they disappear, no matter how stealthily you approach. In their place are peculiar stacked stones and huge rounded masses of rock.

These are our tors (from the Old Welsh "twr" meaning pile or cluster). In shapes ranging from rounded blocks to dancers, turtles, beehives, and potato chips, they inhabit magical places like Vedauwoo, Blair, and the Devils Playground. But why? How and when did such fantastical beings appear?

Pioneering geologist Ferdinand Vandeveer Hayden once admonished humanity for not asking such questions. "Like the ripe fruits which so many pluck from the tree, and enjoy without a further thought, [landscapes] are accepted by mankind, and how few are thoughtful enough to inquire from whence they come!"

But not us, Professor Hayden. We are among the thoughtful few!

Monuments left by erosion, pleasing in their variety

Hayden's complaint appeared in his 1871 Preliminary report of the U.S. Geological Survey of Wyoming, specifically in the section about the Laramie Mountains, which he had crossed by train the previous year. At the crest, he came upon "scenery which is quite unique and remarkable, differing in many of its features from that at any other point along the [rail]road."

It was a landscape dominated by granite, as Hayden explained. The plateau-like summit was "literally paved with small fragments", and "massive piles, like the ruins of old castles, are scattered all over ... the difference in texture of the rock is such as to give a most pleasing variety, hardly any of these piles being alike."

Hayden then turned to the difficult question—from whence they come. "There is an interesting thought just here as to the real origin of these granitic, ruin-like piles that give the peculiar distinction to the plateau surface of the Laramie Mountains. I believe it is entirely due to erosive forces, which have operated here on a gigantic scale, and these cones and natural temples are the monuments that are left to tell the tale."

"I am convinced that the surface was at one time at least on a level with the highest of [the granite piles]." he continued. "How much more has been removed it is now impossible to tell, but I am convinced that comparatively few geologists have fairly estimated the immensity of the time required and the vastness of the amount of material removed from the surface by erosion."

Broadly-speaking, Hayden was correct. The tors of the Laramie Mountains were created by erosion. But there's much more to the story. It seems that erosion played multiple roles—shaping, revelation, and now destruction.

"Skull Rock ... has been peeled off, coat by coat, by the fingers of Time ..." wrote Hayden in 1871. (LOC).

A granite named Sherman

In early August 1907, the Laramie Republican (newspaper) announced the arrival of a "geological savant"—Professor Eliot Blackwelder, of the University of Wisconsin and the U.S. Geological Survey. He would study the surface geology of the southern Laramie Mountains, specifically the oldest rocks of the range.

For regular readers of this blog, "Eliot Blackwelder" may ring a bell. He appeared in a recent post about the Snowy Range, where he also studied ancient rocks. In fact, Precambrian rocks—the oldest on Earth—were Blackwelder's specialty.

Shortly after arriving, Blackwelder recruited an assistant—Herbert Kennedy, of the Republican's business department (he was replaced by his brother, Leon). Two days later, they left to set up their field camp near Tie Siding. They would work into late September, when Blackwelder returned to Wisconsin and Herbert Kennedy returned to his studies at the University of Wyoming.

In 1908, Blackwelder published "Pre-Cambrian rocks in southeastern Wyoming". He named the granite at the crest of the Laramie Mountains the Sherman granite, after the now-defunct Sherman railroad stop. The next year, in text accompanying geologic maps for the area, he described what he considered "the most important event of pre-Cambrian time in this district ... the intrusion of a vast mass of coarse-grained granite."

Rapakivi and grus—killer conversation starters

Like Hayden, Blackwelder was impressed by the small fragments that covered the ground to great thickness. "Although hard in its unaltered condition the Sherman granite disintegrates readily under the influence of descending surface waters and produces a coarse gravelly soil ... In excavations at Buford the granite has been found to be decayed to a depth of 40 to 50 feet ...".

This would greatly benefit the Union Pacific Railroad. The Buford quarry furnished trackbed ballast for 800+ miles of track, from Omaha to Rock Springs. From 1900 to 1914, an estimated 10,000 railcar loads were produced each year. Furthermore, Sherman ballast was cheap—a ton for just 6¢! —while average cost for the region was 49¢ per ton.

UPRR track builders approaching crest of Laramie Mountains on a bed of Sherman grus; 1867-68; Beinecke Library (cropped).

Because it breaks down so readily, geologists classify the Sherman granite as "rapakivi" ("mud rock" in Finnish). If wetted, mica in the granite expands, breaking the rock to create gravel, mainly crystals of feldspar and quartz. Geologists call this kind of decomposed granite "grus" (pr. gruce or sometimes gruss).

Blackwelder all but ignored the other remarkable feature of Sherman granite—the tors. He provided one photo and a single sentence. "Where thus deeply weathered, the outcrops of granite are smoothly rounded and free from visible ledges."

Sherman granite on crest of Laramie Mountains; looking north across "wide rolling plain of the mountain plateau". From Blackwelder's 1909 report (USGS); photographer unknown.

The problem of tors

Tors have long been mysterious and difficult to explain. One of the biggest obstacles is the many kinds, which likely differ in origin. Fortunately, the tors of the Laramie Mountains appear to be very similar to those of England, which have preoccupied humans for millennia. Perhaps their accumulated knowledge will provide some insight into the origins of our tors.

Haytor, perhaps the grandest of Dartmoor tors (southwest England; courtesy Smalljim).

The earliest accounts invoked mysticism and magic. Often tors were said to be living creatures turned to stone during some foolish encounter with a witch or the devil. A magical explanation for our tors would be wonderful, since the geology is complicated and still debated! But it appears there are none available, so we will rely on science.

English antiquarian and naturalist William Borlese of Cornwall may have been the first scientist to study tors. In a 1758 account, he concluded they were human creations, like the obvious constructions at Stonehenge. This was a popular theory for a time, but then geologists intervened.

Early on, geologists suggested that tors were once sea stacks—isolated stone towers just offshore. But sea stacks are angular and jagged, whereas the tors of England (and the Laramie Mountains) are distinctly rounded.

Sea stacks, Victoria, Australia; photo by Sam Abell.

Need to look in surprising places

In the second half of the 19th century, several English geologists made a conceptual leap. They spotted similar forms, not above ground, but in granite quarries! They realized that tors look very much like the quarryman's rounded "corestones" but with the "growan" (grus) removed. These geologists concluded that tors develop underground, where they wait to be revealed, whether by quarrymen or erosion.

In spite of the remarkable similarity of tors and corestones, this theory was largely ignored until 1955. That year, an English specialist in landforms, geomorphologist David Linton, published a paper explaining a process that could sculpt tors underground—"profound rock rotting." Groundwater flowing through fractured granite can break down narrow zones of rock, creating rounded blocks and filling the cracks with grus.

Profound rock rotting seems a likely explanation for our tors, made as they are from rapakivi granite!

Stages in the evolution of tors, by subsurface rock rotting (Linton 1955).

From birth to emergence

By now, readers surely are at the edge of their seats, eager to learn how our tors made it from their subterranean birthplace to the surface. But first we must backtrack 1.43 billion years. That is the estimated age of the Sherman granite, the time when it crystalized from molten magma, the actual birth of our tors. 

They may have remained in their infant form for hundreds of millions of years. Geologists still debate when shaping of the tors took place. The granite may have fractured when it solidified. Or maybe it happened later when erosion at the surface reduced pressure on the granite underground. Or maybe both! Nor is it clear when groundwater reached the fractured granite and began breaking it down. And there may have been several episodes.

We have a better understanding of how and when the tors were finally revealed at the surface. Their emergence is related to the Laramide Orogeny—the great mountain building episode that started 80 million years ago, lasted almost 40 million years, and created mountain ranges from Mexico to Canada—the Rocky Mountains.

It was during creation of the Rockies that the Laramie Mountains were uplifted. Like all mountains, as soon as they began to rise, erosion set in. This was erosion on a grand scale, just as Hayden suspected. After about 35 million years, enough overlying rock had been removed to expose the ancient Sherman granite. Grus in the joints was washed away, leaving behind our remarkable tors.

Visit our aging tors

Erosion hasn't stopped. It continues to slowly expose more tors, but it also destroys the ones we know and love. Wind, rain, and freezing remove a bit more rock every year. Occasionally a block falls! But from our perspective, ephemeral beings that we are, this destruction is incredibly slow. We still have time to enjoy our tors, so let's go!

From Interstate 80 about 15 miles east of Laramie, take the Vedauwoo Road east. Drive a quarter mile beyond the entrance to Vedauwoo Glen (fee area) to a grus-covered parking area on the left (free, with bathrooms). Follow the grus-covered trail past an interpretive sign and Pedestal Rock. Look for low mounds of granite—are these young tors emerging from below? or fallen blocks buried in grus? Curve left uphill and through a gate. Wander to the right across a large slab of Sherman granite. Note crystals of pink and white feldspar, sparkly quartz, and black biotite mica between the patches of lichen. Take in terrific views of tors, pleasing in their variety, just as Hayden said. Explore cracks and gullies to see decomposing rapakivi granite.

The best time to visit is during the golden hour before sunset—the magic hour when the light is warm and soft. You will be tempted to stay longer. But if dusk falls, do take care, lest you too be turned to stone!

Vedauwoo tors during the golden hour, not long before dusk.

This post is based on an article I wrote recently for the Laramie Boomerang's "History" column. In case you're wondering, I don't believe in magic ... under normal circumstances.

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.

Sea Shells in the Church Walls (& other mysteries of the Casper Formation)

 

For geologist and bishop Nicholaus Steno, science was a way to understand God's work (source).

On the morning of August 13,1894, mason Michael Bergin picked up a stone to add to the new Episcopalian church in Laramie, Wyoming. But upon inspecting it, he spotted a fossil very different from the others he had found.

"CURIOUS FOSSIL. Found in the Sandstone Rock of the Cathedral" announced a headline in the Laramie Boomerang (newspaper) later that day. "It is a shell exactly like a miniature buffalo head ... the solid part corresponding to the head is about an inch in diameter, the horns about an inch long and three inches from tip to tip." Bergin set the stone aside for Professor J.D. Conley, curator of the University of Wyoming Museum.

Stonemasons at St. Matthew’s Cathedral regularly found fossils, saving the better ones for Professor Conley. He had already identified the clam-like allorisma, snail-like bellerophon, and pinna, which resembled a razor shell oyster. "The professor is gathering facts to put into a bulletin on the subject," explained the Boomerang.

But the article ignored the remarkable mystery these creatures implied. They were marine—all inhabitants of oceans. Yet the stones were quarried just east of Laramie. How did sea shells end up so far from a sea, and 7000+ feet above sea level?

A Persistent Question

Four centuries earlier, in the Apennine Mountains of Italy, scientist Nicholaus Steno asked the same question, but in Latin: “Quomodo res marinae in locis a mari remotis derelictae fuere?” How was marine life abandoned in places far from the sea?

No answer was immediately forthcoming. In the 1600s, geology did not exist, and knowledge was strongly shaped by church teachings, which did not address things like sea shells high in the mountains. Steno had to rely on field work and his own clever mind to solve the puzzle.

After examining many specimens, all of which looked like sea shells down to the finest level of detail, he concluded they were sea shells, now entombed in rock. They must have risen from sea level, thousands of vertical feet! This meant the surface of the Earth was dynamic, changing dramatically since the Creation. Steno's findings contradicted strict biblical interpretation—that God had created an immutable Earth—but the Church did not object. Science was increasingly seen as a way to understand and appreciate God's work.

Steno's interpretation of an angular unconformity, from his Prodromus, 1671.

Revelations

How appropriate then that St. Matthew’s Cathedral contributed to our understanding of local geology. Specifically, the fossils revealed when the rock formed. "These specimens all serve to identify and locate more definitely [in time] the geological formation of the sandrock lying east of the city ... This is the carboniferous [Period] in the upper Paleozoic [Era]."

But the Boomerang mentioned none of the immense numbers geologists love—millions, hundreds of millions, billions of years. That's because in 1894 there was no way to determine absolute ages of rocks. We now know the Cathedral sandstone formed sometime between 325 and 300 million years ago, when much of southeast Wyoming was submerged.

For millions of years sand, shells, and limey muck accumulated on the floor of that Paleozoic sea. Then they lay buried for several hundred million years more, gradually changed to sandstone and limestone.

The Rocks Rise

While Nicolaus Steno was convinced that rocks could rise thousands of feet, he never came up with an explanation for how. In fact, how mountains rise proved to be a most persistent question. It wasn't until the mid 20th century that it was answered satisfactorily: The Earth's surface consists of giant shifting plates that collide, sink, override, fuse, and more. The effects can be dramatic.

Between 70 and 30 million years ago, the Pacific plate was diving under the North American plate, compressing and crumpling the interior of the continent, creating among other things the Rocky Mountains. With uplift of the Laramie Range, ancient marine limestones and sandstones, carrying fossil shells, rose thousands of vertical feet. Erosion later exposed these rocks, setting the stage for Laramie's promising building stone industry.

Quarrying stone just east of Laramie; date unknown.
American Heritage Center, University of Wyoming (AHC).

Inexhaustible Supply of Rock

On May 11, 1886, the Boomerang proudly announced "Vast Deposits of Sandstone Only Three Miles from Laramie." This was great news. Planning was underway for the University of Wyoming's first building, to be constructed entirely of sandstone. However the nearest quarries were in Rawlins and Ft. Collins; transportation probably would be too costly.

Ever the civic promoter, the Boomerang declared Laramie's stone to be "equal to any in the world. ... It is useless to send to Colorado at great expense for rock which is not one particle superior, either in strength, beauty, evenness ..." The local quarries were inspected, the stone tested. In August, a contract was signed. The University Building (today's Old Main) rose quickly, completed in time for the first classes in September 1887.

Old Main under construction, University of Wyoming, ca. Dec. 1868 (AHC).

Though the industry never became a booming business, Laramie's dimensional stone was used in local buildings into the 1950s. These included the Albany County Courthouse, Ivinson Mansion (Laramie Plains Museum), Ivinson Home for Ladies, many buildings on campus, and perhaps most spectacularly, St. Matthew's Cathedral.

"One of the Most Beautiful and Complete Churches in the entire Western Country"

In 1892, on September 21 (St. Matthew's Day), the Boomerang gave front-page coverage to the laying of the cornerstone of St. Matthew's Cathedral. In the recently completed basement, hundreds listened to distinguished clergymen speak eloquently and at length. Then three officers from the Grand Lodge of the Free Masons—equipped with square, level, and plumb—set the stone.

St. Matthew’s Cathedral as originally planned; the final was somewhat smaller. Laramie Boomerang, Sep 22, 1892.

It was said that the Cathedral would be completed within a year. But the walls would rise in spurts, as funding waxed and waned. Bishop Ethelbert Talbot traveled far afield in his fund-raising. Big donors included friends in the east, such as Cornelius Vanderbilt ($1500) and J.P. Morgan ($1000), and the Mother Church in England.

By the end of 1896, the grand structure was ready to serve its congregation and was dedicated before a crowd of almost a thousand on December 17. Twenty years later, Edward Ivinson made a large donation in memory of his wife, Jane, to finish the towers.

St. Matthew's Cathedral before towers were completed (in 1916); photo ca. 1910-1915 (AHC).

St. Matt's in 1935 (AHC).

According to common knowledge, the cathedral stones came from the university quarry, nine miles northeast of Laramie. But an 1894 Boomerang article about a proposed railroad building suggests otherwise. Planners noted that cathedral stone was less expensive than university stone, as the cathedral quarry was closer to town. But which of today's abandoned quarries it was remains a mystery.

Adding to the puzzle is confusion regarding rock type. Cathedral descriptions variously refer to limestone, silicious limestone, limey sandstone, or sandstone. The Casper Formation, where Laramie's quarries were developed, contains all of these.

Reading the Casper Formation

To a geologist, a formation is a group of rocks that is both recognizable and extensive enough to map. The Casper Formation extends from Casper Mountain south along both sides of the Laramie Range into Colorado. It's a mix of limestone, sandstone and everything in between. Herein lie important geological clues!

Geologists say they study the past by "reading the rocks." What have they learned by reading the Casper Formation? We already know from its fossilized sea shells that there was an ocean here 300 million years ago. But there's more.

Let's start with limestone, which forms from limey muck deposited in deep water far from shore, out of reach of sediments from land. The northern part of the Casper Formation is dominated by limestone, indicating the area around the towns of Casper and Douglas was submerged in deep water during much of the Paleozoic Era (tour map below shows features mentioned here).

But in the Laramie area, the Casper is mainly sandstone with occasional beds of limestone. Sand, being coarse, doesn't travel far, so sandstone is a sign of shallower water closer to shore. The limestone beds are a bit of a mystery, with geologists still debating the details. Most likely they formed when the sea advanced, perhaps with rising sea level. So Laramie probably was in deep water occasionally, the shoreline farther away.

The Casper Formation also contains clues about the shoreline itself. Not far south of Laramie are outcrops of cross-bedded sandstone (criss-crossed layers). These are remains of sand dunes deposited by wind along the ancient shore.

Just beyond the dune field was the Ancestral Front Range. We know of these ghostly mountains because the Casper sandstone contains abundant feldspar. Feldspar is a soft mineral that breaks down quickly. It must have been carried to the sea by fast-flowing streams from mountains close by.

Tour Paleozoic Laramie

Yellow very roughly outlines the Casper Formation (above and below ground).

With an able imagination, you can tour the Laramie area 300 million years ago. Start in a dune field at the foot of the Ancestral Front Range. Venture into shallow waters of the Paleozoic sea and then to its depths. At the final stop, careful beach combing should turn up some of its ancient inhabitants.

1. Sand Creek National Natural Landmark straddles the state line along Sand Creek Rd. (CR 34; gravel) about 19 mi south of Laramie. Amidst monuments and hoodoos of cross-bedded sandstone, imagine yourself in a field of dunes at the base of a rugged mountain range, looking north across the Paleozoic sea. The Landmark is mostly private with two small parcels of WY state land; an ownership map is needed to explore beyond the road.

"Grotto at Sand Creek"—S.H. Knight photo, 1899 (AHC).

2. Visit Roger Canyon to see the Paleozoic seafloor up close. From Reynolds St. in Laramie, go north on 9th about 0.7 mi to where it becomes Roger Canyon Rd. ZERO YOUR TRIP ODOMETER HERE. At 6.9 mi ("No Winter Maintenance" sign) stop in the tiny turnout right (private land; stay on shoulder). Across the road is the reclaimed university quarry. Here the Casper is limey sandstone (well-cemented). Head up the canyon. At 8.0 mi, you will enter public land and limestone—having traveled back in time to when the water was deeper and the seafloor covered in limey muck. Public land continues for about a mile.

Chris and Ed of Laramie brave the smokey air to ascend lithified seafloor muck in Roger Canyon.

3.  St. Matthew's Cathedral stands on the northeast corner of Ivinson and 3rd. Wander the grounds to admire Laramie's fine dimensional stone in the walls of the highest Cathedral in the US (steeple reaches 7276 feet above sea level). Search for sea shells in the exterior stone, but please don't touch (binoculars are handy).

About that Miniature Buffalo ... any ideas?

Professor Conley reportedly left Laramie in a huff in 1896, having been passed over for department head. The fate of the Cathedral specimens is unknown, and no bulletin was published. Michael Bergin’s curious fossil remains among the mysteries of the Casper Formation ... unless you recognize it. If so, please leave a Comment below!

This is my latest contribution (with extra photos) to the Laramie History series in the Laramie Boomerang (published August 30, 2020).

Stink Lake in a Sink Hole & other marvels of gypsum

“Laramie from the air – 1932”, looking roughly north. Arrow points to today’s LaBonte Lake; the smaller lake to the west is now filled. Courtesy Laramie Plains Museum.

If you've lived in Laramie long, you must know LaBonte Lake—the pretty little pond in LaBonte Park, west of 9th St. between Canby and Shields. On fine summer days it sparkles in the sun, a blue gem set in green grass. But have you ever noticed that no stream flows in or out? Have you ever wondered why there’s a lake there at all?

The explanation lies well below the sparkling surface, below the haunts of the salamanders that migrate to and from the lake in spring and fall, even below the lake-bottom muck, rich in tiny creatures whose heady breath gives the pond its other name—Stink Lake. The explanation resides deeper still, in the convoluted tunnels and chambers that wind through Laramie’s gypsum-rich dirt.

Ancient seas to toothpaste and pyramids

Most of us are familiar with gypsum. It surrounds us in plaster and sheet rock, and is an important component of toothpaste and concrete (portland cement). It forms casts for broken body parts, and is widely-used as a soil amendment. Builders of Egyptian pyramids filled gaps between their rough-hewn stones with gypsum plaster.

Gypsum is a mineral so soft that it can be scratched with a fingernail, occurring in forms ranging from powder to rock. It starts as calcium and sulfur dissolved in saltwater. These chemicals react to form gypsum if the saline water undergoes enough evaporation—that’s why gypsum is said to be an evaporite.

Wyoming was a great place for evaporites 200-300 million years ago. A shallow sea repeatedly covered the region, and sea level rose and fell many times. Often when the sea dropped, it left behind mineral-charged isolated bodies of water. Apparently there was plenty of evaporation, for gypsum crystallized out forming thick deposits on the sea floor.

During the millions of years that followed, these gypsum deposits were buried and became rock under the pressure of hundreds of feet of sandstone, limestone and shale. Later, when the Rocky Mountains were uplifted, erosion removed enough of the rock cover to the expose gypsum in places, for example on the west flank of the Laramie Mountains. This was noted by newspaperman Leigh Freeman in 1868.

“Observe the splendid beds of gypsum”

That spring, the Union Pacific Railroad reached the Laramie Plains on its race west to complete the great Transcontinental Railroad. Construction crews arrived in April, accompanied by their entourage of merchants, saloon operators, gamblers, prostitutes, and a “press on wheels”—The Frontier Index. The Index was Laramie’s first newspaper, but only until July, when it relocated to Green River.

In the April 21 issue, editor Freeman extolled the virtues of Laramie in an article titled The City on the Plains: “The railroad towns between Omaha and the Rocky Mountains … are alive and flourishing, but none of them have one-hundredth part of the natural advantages that Laramie boasts of. Look yonder at those heavy bodies of timber; take a glimpse of the iron and copper graves that dot the whole country over, see the coal cropping out from one end of the plains to the other; observe the splendid beds of gypsum …”

Rock gypsum at Red Butte

Uncharacteristically, Freeman was accurate about Laramie’s gypsum. It truly was “splendid” and would serve Laramie well for some fifty years. The first quarry opened in 1890, its significance later noted by State Geologist W.C. Knight: “Gypsum was first developed in Wyoming 10 to 15 years ago at Red Butte station, on the Union Pacific Railroad, about 9 or 10 miles south of Laramie … the only [place in the state] where the known, gypsum-bearing beds were crossed by a railroad.”

Rock gypsum quarry at Red Butte south of Laramie, Wyoming, May 1891.
Courtesy American Heritage Center, University of Wyoming (AHC).

The gypsum at Red Butte is rock gypsum—lithified deposits from Wyoming’s ancient seas. Though hard enough to be called ‘rock’, it’s easily ground into a powder, the first step in processing. This rock gypsum also underlies much of Laramie, but hundreds of feet underground where it causes little trouble.

Gypsite fine enough to plow

In the mid 1890s, a more valuable form of gypsum was discovered just south of Laramie, in the Spring Creek drainage. It was gypsite—a crumbly material produced by weathering of rock gypsum, probably by water or wind.

Unlike rock gypsum, the gypsite did not have to be ground, which made plaster production more profitable. “The Laramie gypsite … is as fine as powder, requiring no grinding or even sifting. It is plowed, harrowed and scraped up, calcined [heated to make plaster], and loaded on the [railroad] cars,” reported the Laramie Republican in 1920.

“Plowing stucco” (mining gypsite) near Laramie, December 24, 1906. Courtesy AHC.

Plaster mill near Laramie, ca. 1890-1910. Courtesy AHC.

From Laramie Republican newspaper, February 26, 1921.

At that time, gypsite plaster manufacturing was one of Laramie’s bigger industries. Two mills produced 310 tons daily, and plaster was shipped to 20 states in the western U.S. But with the discovery of larger deposits elsewhere in the country, Laramie’s gypsite plaster industry came to an end; the last mill closed in 1948. Even so, gypsite is still very much with us.

Gypsite made LaBonte Lake … & more

Two extensive gypsite deposits underlie Laramie (see aerial photo near end of post). One is north of the University, the other in the Spring Creek drainage (site of the old quarry and plaster mill). Sometimes gypsite is visible at the surface, as patches of whitish soil associated with stands of greasewood, a salt-tolerant shrub. More often it’s several feet below ground, out-of-sight. But with enough water, gypsite will reveal itself.

Gypsite is water-soluble, not surprising given its origins. Flowing groundwater easily dissolves gypsite, creating tunnels and chambers—a topography called ‘karst’ (cavers know this word). Well-developed karst can be completely hidden, with no indicators at the surface. But if enough gypsite is dissolved and removed, the ground will collapse to form a sinkhole—like the one containing Stink Lake.

Some claim LaBonte’s basin is an old gypsum quarry, but studies point to gypsite-caused collapse. In 1983, borings were taken from the lake bottom to evaluate stability (a plan was afoot to build an island for picnicking). Six years later, more cores were taken from the lake west to 4th St., to assess hydrocarbon pollution. Both studies showed downwarped strata forming a concave structure, consistent with sinkhole formation. However, aerial photography from 1947 shows what might be a gypsum stockpile just northeast of the pond. Perhaps the sinkhole was enlarged with quarrying.

LaBonte is not the only sinkhole in the neighborhood. Early maps and a 1932 aerial photo (see beginning of post) show a second pond to the west. By the 1940s, it was being filled with trash—the city dump. When the dump was moved to its current location, more fill was added. The old pond is now overlain by softball fields and City buildings.

Living with gypsite

Not all sinkholes in Laramie are as charming as the one that holds LaBonte Lake. More often, they pose significant risk to people and property, especially when they develop abruptly: a cavernous pit that opens in the backyard, a car that breaks through the garage floor overnight, roads and buildings that suddenly collapse when the ground beneath sinks.

Sudden collapse in a Laramie alley underlain by gypsite. Foster White photo, date unknown.

Gypsite tunnel in Laramie, with Foster White for scale. Todd Jarvis photo, 1994.

Rotting basement foundations, buckled sidewalks, ruptured utility lines, and blistered potholed streets are other signs that devilish gypsite karst lurks below. Problems often grow with investigation. A shovel can reveal cavities 10 feet deep or more, tunnels big enough for a person to crawl through, and dense networks of water-saturated passageways suggesting imminent collapse.

We can’t blame natural groundwater alone for these problems. Often we’re the ones that introduce water to gypsite, for example by watering our yards (tree roots deliver water to karst quite effectively). Stormwater draining off our streets can rapidly enlarge karst features, as can leaking old or inadequate pipes.

Gypsite’s impact on Laramie is significant. For example, in 2008 the City repaired 140 emergency pipeline breaks, whereas the regional annual average was 50 to 80 repairs according to the American Water Works Association. And consider Palmer St.: Since 1988, when record-keeping began, gypsite corrosion of cast iron pipes has caused 15 mainline breaks in just two blocks. The City now requires cast-iron-equivalent PVC pipe in gypsite areas, but does not otherwise factor gypsite into planning.

For more information about Laramie’s gypsite, get the Wyoming State Geological Survey’s 2016 publication, Evaporite Karst Features in the Southern Laramie Basin (free online). Our two gypsite areas are indicated on the aerial photo in Figure 6 (below).

From Ver Ploeg et al. 2016 (color/symbol key added). Olive green areas have gypsite deposits.

If you haven’t already experienced Laramie’s gypsite dirt and would like to, then explore the Spring Creek floodplain west of 9th St., or drive Bill Nye Ave. west of 15th (gravel). Look for spindly greasewood shrubs and white-crusted dirt. But tread carefully, for karst may lurk just below your feet! Your fate could be similar to that of the Laramie boy who fell off his bike into gypsite mud. He was stuck waist-deep for hours until the fire department finally got him out.

Credit where credit is due

Thanks to former longtime Laramie resident and geologist Dr. Todd Jarvis, who suggested this topic and provided much of the information. Jarvis is a sinkhole sleuth and water folklorist now practicing in Oregon. Thanks also to Foster White of the South of Laramie Water and Sewer District, for sharing his stories about the marvels of gypsite.

[This blog post is a modified version of an article published in the Laramie Boomerang on March 1, 2020. The post includes sources and many more images.]

Sources

Jarvis, T., and Huntoon, P.W., 2003, A stinking lake and perpetual potholes: living with gypsite karst in Laramie, Wyoming, in Johnson, K.S., and Neal, J.J. (eds.), Evaporite karst and engineering/environmental problems in the United States: Oklahoma Geological Survey Circular 109, p. 263-269.

Knight, W.C., 1904, Gypsum deposits in Wyoming, in Adams, G.I. et al., Gypsum Deposits of the United States. USGS Bull. 223.

Ver Ploeg, A.J., Larsen, M.C., and Taboga, K.G., 2016, Characterization of evaporite karst features in the southern Laramie Basin, Wyoming: Wyoming State Geological Survey Report of Investigations 70, 33 p. (free download)

Old newspapers provided by Wyoming Newspapers (Wyoming State Library).

A Different Tree (actually a different location)

By the shores of Lake LaBonte, by the shining snow and ice ...

I changed my mind about tree-following. I won't be at the Art Building on the university campus again, but at LaBonte Park. I haven't decided a tree yet, just the location.

In case you're new to the concept, tree-following means checking a tree once a month, and reporting on it at the virtual gathering kindly hosted by The Squirrelbasket. We choose a different tree each year (if we want, the rules aren't rigid). This project was started by Lucy Corrander eight or nine years ago (if I remember right). I was quickly hooked. It's fascinating! Consider joining us (more here).

LaBonte Park is a small park in town with a pond called LaBonte Lake. It was this lake that drew me to the park, for it has mysterious origins. Old timers say it was a quarry. Geologists attribute it to the convoluted system of caverns and tunnels that lurk below. I like the second hypothesis. Surely there are elves, fairies, gnomes and such in the catacombs. They must have an explanation too, and a good one.

The park has plenty of trees, but most look to be the usual landscaping varieties: poplars, cottonwoods, hawthorns and lots of conifers—mainly spruce with some pines.

Above and below: a healthy spruce on the shore of LaBonte Lake.

But then I spotted something different, and a likely candidate for tree-following.

Even though the leaves were dried, curled and wind-tattered, it was clearly an oak. I like trees I can identify!

Early on my stroll through the park, I saw a man cross-county skiing on the thin snow and big patches of bare grass—so odd, even funny! But I didn't stare. Then I realized ... he was simply on his way to the lake, where he took off skiing near shore (shallow water sure to be frozen).

Later I spotted him halfway around the pond.

It was neat to see ski tracks winding through emergent wetland plants. I would love to try this! Maybe next month ...