In our 30-second sound-bite, social media culture the phrase “the old west” may get confused for “Old Navy.” But for those old enough or who have studied US History, the phrase may conjure images of cowboys, Indians, wagon trains, and gunfights. But the period of the cowboys and cattle drives, the US Cavalry and plains Indians, gunfights and outlaws, only lasted one generation, from the end of the mid-1800s to the end of the 1890s. Nowadays, much of the prairies and plains are neatly arranged in arbitrary rows of corn and wheat, oats and soybeans, edged and dissected by ribbons of concrete and asphalt. The real old west, particularly from the Mississippi to the Rockies, the west in which the plains bison evolved, has a much larger and dramatic history; perhaps more than our feeble recollections can grasp. Understanding bison evolution depends on an awareness of the geological and environmental history of the “real old west.”
From the mid-Cretaceous Period—145 MYA (millions of years ago) to 66 MYA—to the very beginning of the Paleogene Period (66 MYA to 23 MYA) the earth sported a shallow sea. Known as the Western Interior Seaway, it was located in the middle of what is currently the North American continent, roughly splitting that land mass in half.
Hidden underneath the earth’s crusty surface, however, a great struggle was taking place. The tectonic war that had begun since the earth’s infancy was pushing up stone giants to the west of the sea and tilting the seabed, sloping downward from west to east. The result was the formation of the Rocky Mountains (80 MYA – 50 MYA), known as the Laramide Orogeny . During this time, the sea drained revealing a soil-rich plain.
However, the tectonic struggle was not the only force imposing its will on the North American land mass. Cold and warm played a tug of war with glaciation advancing and retreating many times throughout the Pleistocene Epoch—2.6 MYA to 11,600 yrs. BP (Before Present). During one of those glacial periods—the Mindel Glaciation lasting from 0.5 MYA to 125,000 yrs. BP—the Bison genera reached northern Eurasia and by way of the Bering land bridge (Beringia) two of the species spread into North America as far as present day Mexico .
Bison antiquus was most common in the southwestern US and Mexico, while Bison latifrons was found primarily north and inhabited a more heavily wooded or forested environment. B. Latifrons became extinct during the late Wisconsin glaciation (around 11,000 yrs. BP), while B. antiquus survived into the current Holocene epoch during which it evolved into the modern species of Bison bison consisting of two subspecies—B. Bison bison (Plains bison)and B. Bison anthabasca (Woods Bison).
Vegetation development and movements accompanied the withdrawal of the glaciers. The general withdrawal began after 14,000 yrs. BP and most or all of the ice had disappeared by around 6500 yrs. BP. During this time, within the region encompassed by the present day Great Plains and bordering prairies, forests and wooded areas were widespread with little open vegetation. More open vegetation developed during the interglacial periods.
The Holocene vegetation pattern developed in response to the general continental warming and drying trend that occurred between 11,000 yrs. BP—the end of the Wisconsin glaciation and the beginning of the current Holocene epoch—and 7000 yrs. BP. The central grassland began to form during the very late Wisconsin glaciation and reached its maximum extent around 7000 yrs. BP .
Meanwhile, the stone giants of the Rockies, sitting silently to the west, formed a rain shadow over the exposed ice-free former seabed, inhibiting needed rain from falling upon the western most regions of the vast plains. The storm clouds that made it passed the rocky sentinels would not drop their precious cargo until further east. Eastward from the Rockies the land slopes downward, while the rainfall follows an inverse slope. This factor is significant in the evolution of the grasses. Not enough rain was allowed for forests, but more than enough to prevent a desert. The mighty forests, found further east, were denied. Even bushes and shrubs were hard-pressed. Of course, a lone tree or a small gathering of bushes here and there may have taken hold along a river or creek, but the land was to be ruled by grass, and aridity became the first and most implacable factor .
Closest to the majestic sentinels on the western horizon arose the short grasses while in the east where the dawn’s first light strikes, and the clouds are more willing to release their precipitation, arose the stately tall grasses. This aridity gradation drove the developmental effort of the grasses to be concentrated in the root structures, driving deep into the soil, holding the soil against an unrelenting wind sweeping across the plains. Thus deep-rooted perennials, both of the short grass and tall grass varieties, took hold. Inextricably tied to the development of the open vegetation of this vast great plain was the evolution of the bison. The Great Plains and the plains bison came into being together.
Long before there were wagon trains and US Cavalry, cowboys and gunfights; long before Europeans were even aware of the North American continent, there existed a vast history of land and vegetation movements vying for dominance of a great region. But it was not just a drama of earth and flora. Old species of fauna disappeared to be replaced by new ones. Humans were present as well—the ancestors of the Native Americans who, in this relatively new region, came to depend on one of the new species of fauna—the Plains Bison. The Holocene Epoch is the real old west mocking our current understanding of the old west, and to which, our social media apps culture is not even a blink of the eye.
 The Laramide orogeny was a period of mountain building in the western portion of present-day North America. This period started in the late Cretaceous, 70 to 80 million years ago, and ended 35 to 55 million years ago. The word “orogeny” is a geological term pertaining to the process of mountain making or upheaval (Webster’s Unabridged Dictionary).
 McDonald, Jerry N. 36. 2016. North America Bison: Their Classification and Evolution. McDonald & Woodward Publishing Co. Newark, Ohio.
 McDonald. 22-28.
 Manning, Richard. 3. 1995. Grassland: The History, Biology, Politics, and Promise of the American Prairie. Penguin Books.