Hepburn's Mesa
By editor
Pray, Park County, Montana, July 2021
The black-capped bluffs located on the east side of the Yellowstone River are called Hepburn's Mesa. The mesa is capped by a basalt lava flow the erupted from a small local volcano vent that has long since eroded away. Geologically, the lava flow is very young, perhaps having erupted as recently as 2.2 million years ago. Large amounts of iron in the basalt make it dark colored. She of the iron crystallized as magnetite, which as the name implies is magnetic, and in large concentrations can cause compasses to behave erratically. The basalt flow overlies unconsolidated gravels, which in turn overlies older light-colored fine-grained sedimentary rocks that were deposited in an ancient lake that once occupied this site. The sedimentary beds of Hepburn's Mesa contain abundant Miocene fossils, including ancient rodents, moles, and a porto-horse called Merychippus, the first equine to exhibit the distinctive head of today's horses. On top of Hepburn's Mesa, overlying the basalt is glacial till of Pleistocene age. The surface these deposits is hummocky and is littered with abundant glacial erratic boulders. For generations, Native Americans drove bison off the mesa's cliffs to obtain food, hides, and other materials important to their way of life.
Hepburn's Mesa is named for John Hepburn, a local rancher, rockhound and amateur paleontologist. He arrived in the Emigrant area in 1909 after working in Yellowstone National Park for many years. From 1935 until his death in 1959, he operated a museum next to Secondary Highway 540 that displayed many of the geologic specimens and fossils he had found in this area. The museum was a local landmark for many years. It still stands next to the old highway and is listed on the National Register of Historic Places.
The geological history of Hepburn's Mesa is a testament to the violent and transformative forces that have shaped the American West. The dark, basaltic cap, a remnant of a relatively recent volcanic eruption, stands in stark contrast to the older, lighter sedimentary rocks beneath it. This juxtaposition of fire and water, of lava flows and ancient lakes, is a vivid illustration of the dynamic nature of the earth's crust.
The presence of magnetite in the basalt, capable of confounding a traveler's compass, adds an element of mystery and danger to the landscape. It is a reminder that the natural world is not always benign or predictable, and that those who venture into it must be prepared for the unexpected. The mesa itself, with its sheer cliffs and commanding views, is a formidable presence, a silent witness to the passage of time.
"The sedimentary beds of Hepburn's Mesa contain abundant Miocene fossils, including ancient rodents, moles, and a porto-horse called Merychippus, the first equine to exhibit the distinctive head of today's horses." This rich fossil record provides a fascinating glimpse into the distant past, a time when the climate and ecology of the region were vastly different. The discovery of these ancient creatures, preserved in stone for millions of years, is a triumph of scientific inquiry and a source of endless wonder.
The human history of the mesa is equally compelling. For generations, Native Americans utilized the sheer cliffs of the mesa as a buffalo jump, a vital source of sustenance and materials. This practice, born of necessity and intimate knowledge of the landscape, is a poignant reminder of the deep connection between the indigenous peoples and the natural world.
The naming of the mesa for John Hepburn, a local rancher and amateur paleontologist, is a fitting tribute to a man who dedicated his life to uncovering the secrets of the earth. His museum, a local landmark for many years, served as a repository of knowledge and a source of inspiration for generations of visitors. It is a testament to the power of curiosity and the enduring appeal of the natural world.
As we stand before Hepburn's Mesa today, we are confronted with a landscape that is both ancient and ever-changing. It is a place where the forces of geology and the hand of man have intersected in profound and unexpected ways. It is a monument to the resilience of life and the enduring power of the earth.
The story of Hepburn's Mesa is a story of discovery and understanding, of unraveling the mysteries of the past and appreciating the wonders of the present. It is a story that challenges us to look beyond the surface of things, to seek out the hidden truths that lie beneath our feet. It is a story that is as vast and complex as the landscape itself.
See also
- Hepburn's Mesa at Pray, Park County (Montana Department of Transportation, erected 2021)
- Yellowstone National Park for more on the region's volcanic history
