Those hardy enough to hike into some of Wyoming’s more rugged terrain near Burgess Junction in Bighorn National Forest are likely to come across something that just doesn’t seem natural.
The giant 75-foot-tall square boulder looks like a huge cube of stone cut from a quarry, or maybe left by ancient alien visitors to Earth.
But it’s all natural, and one of the Cowboy State’s most unique landmarks.
Called Falling Block, this boulder is a cut above the rest of the massive rock formations that can be found in the Bighorns.
It’s a single slab of sedimentary rock with sheer, smooth faces and corners. At first glance, it looks like a perfect cube of stone in an otherwise rugged landscape of irregular shapes and surfaces.
A skeptical mind might see conspiracy in its shape, and many do. Several websites feature Falling Block as the manifestation of unexplained extraterrestrial or supernatural forces.
“I get a kick out of that stuff,” said retired geologist Mark Fisher. “If you look right above the Falling Block, you can see where it broke loose and slid down. There's nothing all that weird about it except that it's so large.”
While its origin is terrestrial rather than extraterrestrial, Falling Block is still worth the attention and intrigue it gets, said Fisher. Even in a state renowned for its geology, he has not seen anything like it in Wyoming or even the world.
“I've never seen one that big and that square,” he said.
Bottom To Top
Falling Block is an immense piece of limestone from the Bighorn Dolomite, a rock formation widespread in the Bighorn Mountains and other parts of Wyoming. It was formed roughly 450 million years ago during the Ordovician Period.
Today, Falling Block is more than 8,000 feet above sea level in the Bighorn Mountains. However, dolomite only forms at the bottom of low-oxygen saline lagoons, which means the high-elevation block once sat at the bottom of the sea.
“It’s a fairly common sedimentary rock made of calcium, magnesium and carbonate,” Fisher said. “It was deposited on the west coast of North America, where the marine water was between a few feet deep and several hundred feet deep.”
After 450 million years of mountain uplift and continental movement, the prehistoric sea floor was elevated to its lofty position. However, Fisher said evidence of the block’s lowly origins is “written” into the rock.
“The surface is bioturbated,” he said. “That’s a term geologists have for sediment churned up by the critters living in softer sediments. Worms, mussels, brachiopods and other organisms were constantly eating through the sediment.”
During the Ordovician, trilobites and brachiopods lived in the salty waters covering Wyoming. The Falling Block might not preserve the body fossils of its former occupants, but evidence of their existence is preserved in its bioturbated surface.
About Those Edges
The origin of the rock itself might be fascinating, but Falling Block stands out because of its eerily perfect edges. Nevertheless, Fisher said the block’s cubic shape could also be explained by ordinary and completely explainable geologic processes.
“Limestones and dolomites like this have horizontal bedding planes,” he said. “When the rocks fall off a cliff, they usually break along these bedding planes.”
Bedding planes determine how sediment is deposited and how sedimentary rocks break in a horizontal direction.
Fisher said that Falling Rock is so intriguing because there aren’t any evident bedding planes. It fell and has remained largely intact because the bedding planes that ordinarily would have broken it apart have been “removed.”
“After falling off a cliff, these blocks usually split into a zillion pieces,” he said. “This thing hasn’t, and it’s immense.”
Fisher said there’s also no evidence of faulting and folding in Falling Block and the Bighorn Dolomite. Those are the multimillion-year processes where external pressures bend and twist rock formations, creating vertical cracks.
Despite its appearance, there’s nothing exceptional about the processes that created it, except that it’s remained large and in charge.
“It's pretty amazing how big this thing is,” Fisher said. “There are no vertical cracks in it, and there are not horizontal bedding planes where it's busted up. I've never seen a block that big that’s remained intact.”
Be There, See Square
Despite its legendary status as a uniquely sized and shaped monolith in the Bighorn Mountains, there are no marked trails to lead curious spectators to Falling Block. But it’s not hard to find, provided you’re prepared.
Fisher has hiked to Falling Block, taking a short drive from Burgess Junction to a parking lot at the end of U.S. Forest Service Road 159.
“It's a mile each way and climbs around 600 vertical feet,” he said. “There's no formal U.S. Forest Service trail to Falling Block, but you can tell people have hiked up there.”
Fisher plotted his route and shared it on the website Geology of Wyoming, which he manages and updates with several other geologists.
Climbers might already know about the legend of Falling Block. While information on it is scarce, Fisher said climbing hardware was = bolted into the block, bottom to top, when he last visited.
“It'd be good to look at it on Google Earth or a topographic map before you go,” Fisher said. “You are walking cross-country, and you need to know where you're headed, but it's not that difficult to reach it.”
A Cubic Crowd
In many ways, Falling Block isn’t unique. Its size makes it stand out among the many unique geological features in Wyoming, but that cubic crowd could get crowded in the future.
By looking at the cliff where Falling Block fell out, Fisher could see more precariously perched sections of Bighorn Dolomite that could topple down the mountainside. If they also have smooth sides there could be a clutter of giant cubic blocks around Falling Block.
“Over the next thousand years or so, more blocks will slide down,” he said. “Maybe they won’t be that big, but there will be others. But I’ve seen plenty of big blocks on a cliff still attached to the wall. I’ve never seen a block as immense and still intact as Falling Block.”
Andrew Rossi can be reached at arossi@cowboystatedaily.com.
