Montana Governor and First Lady's Math and Science Initiative
Hepburn's Mesa
Mile Post 24 on US Highway 89, Emigrant Rest Area
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 that erupted
from a small local volcanic 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. Some of
the iron crystallized as the mineral 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 overlie older lightcolored
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 proto-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 of 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
A Brief History
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.
