The magnificent American bison is the largest land animal in the Americas. 
The largest land animal in the Americas
American bison are magnificent creatures, and they are huge. They are relatives of cattle, and are the approximate size of the very largest cattle breeds. Males can weigh well over 2,000 lbs (900 kg).
The species nearly went extinct in the late 19th Century. In 1890 there were only 750 individual bison left, and this was caused by humans, primarily through hunting and diseases spread from domesticated cattle. Fortunately today their numbers have risen into the hundreds of thousands, although hundreds of years ago they numbered in the tens of millions and lived throughout a very large portion of North America.
Seeing these animals in person is quite an experience. They really are amazing, and after sharing a story about encountering a wild herd in South Dakota, I’ll share information about how many herds are actually genetic hybrids between bison and cattle – and where the last remaining genetically pure herds are located.
Besides the experience in South Dakota, I have also seen wild bison on Santa Catalina Island in the Pacific Ocean near Los Angeles, California. The Catalina herd is one of many wild herds that exist that actually consist of bison-cattle hybrids.
The herd at Wind Cave National Park numbers a few hundred animals. 
Story about seeing American bison in South Dakota
I saw a wild herd of American bison on a vacation with my dad in the summer of 1996. I was seventeen years old at the time, and we were driving from Colorado to South Dakota, visiting many amazing and interesting locations. We visited Wind Cave National Park, mostly to see the fascinating geology of some of the USA’s best caverns, but also to see one of the largest free-roaming bison herds in the world.
I remember that the speed limit seemed low, lower than what a bison could run. The herd numbers more than 300 animals, and we began to see some of them, and then they were closer to the road, and then we decided to stop because a large male was standing right at the edge of the road, and we deemed it unwise to risk running into him.
We stopped our pathetic little rental car, a Geo Metro, which only weighed about 1,800 lbs (800 kg). Adding me and my dad, and our stuff, it was closer to 2,250 lbs (1,020 kg). Even still, the male bison might have outweighed us. We stayed quiet as he took his leisurely time walking right past our car. If the window next to me had been down, I would’ve been able to touch him. He kept walking, slowly, and we hoped he wouldn’t have any reason to get mad at us.
Although this animal was certainly accustomed to people driving though and taking a look, we knew he probably could have tipped our car over if he really wanted to.
I know now that the herd I got to see was extra special because it is one of the few that are left that are genetically pure, without any cattle genes.
Part of the herd at Yellowstone National Park, grazing next to a hot spring. In total there are several thousand bison at Yellowstone National Park, about ten times as many as exist at any of the other locations that have purebred animals. 
Genetically pure bison versus those with cattle genes
Of the estimated 500,000 American bison in the world, it is estimated that about 20,000 or so are genetically pure and not actually bison-cattle hybrids. In other words, probably 95% or more of the world population have at least some cattle genes due to interbreeding of the two species.
The appearance of the animals is an unreliable method for determining whether a bison is purebred or not, because those with cattle genes very often are totally indistinguishable from purebreds. This makes DNA analysis necessary, although the various testing methods also have limitations.
Genetically pure wild herds on public lands (that can be visited by anyone) are found only in the following locations in North America:
- Elk Island National Park in Alberta, Canada (over 300 bison)
- Henry Mountains in Utah (300 to 400)
- Wind Cave National Park in South Dakota (300 to 400)
- Yellowstone National Park in Wyoming (over 4,000)
Bison in Elk Island National Park in Canada. The national park is located near the middle of the Canadian province of Alberta, and is not located on an actual island. 
The herd found at this location is unique because it consists of wood bison, which are one of two subspecies, the other being plains bison. This is the only genetically pure wood bison herd in the world. The other locations listed above are of the much more common plains bison subspecies. 
Why do people call them buffaloes?
Americans typically call them “buffaloes.” However, the two true buffalo species are the Asian water buffalo and the African buffalo. On the other hand, there are two bison species. The American bison is one, and the other is the European wisent, which looks very similar.
The term “buffalo” being used for American bison originated with French fur trappers in the 17th Century. The term was used for well over a century before the more correct term “bison” was ever used at all. The fact that the North American animal is a bison was first known in 1774, although well over two centuries later I still hear people call them buffaloes the vast majority of the time.