I have an approximate migration map here. There are three major routes to the Americas. The first one that is uncontested is the Clovis area. But there are two other sites that predate Clovis, one found in Virginia (or West VA. I forget...) and the other in South America. So I'm going to include those as well.
Horses would follow the earliest peoples across Beringia, but they were small, not really horses. An early equine ancestor is what it is. (Plus an ox-like animal) It would also migrate, and, finding the rugged tundra of Alaska and whatnot too rugged, they would go south. The Canadian plains were covered mostly by glaciers then, so the equines would go further south, finding beautiful open plain. Plains=lotsa grass=high equine population. So the Clovis people would evolve with many horses and oxen about them. I have circled the area in gold. The horses would fan-out from there, eventually maing its way to the banks of the Rio Grande, go both east and west, and after a very long time probably make it to the Andean highlands. However, those equines in high areas (Rocky Mountains, Andes) would be smaller, so perhaps horses wouldn't take very well there.
So the way I see it, the Clovis, Messisippian, and whatever cultures border the Great Lakes and Hudson river would become predominant in North America. Then we have to consider what happens post glacier-melt...
Horses would follow the earliest peoples across Beringia, but they were small, not really horses. An early equine ancestor is what it is. (Plus an ox-like animal) It would also migrate, and, finding the rugged tundra of Alaska and whatnot too rugged, they would go south. The Canadian plains were covered mostly by glaciers then, so the equines would go further south, finding beautiful open plain. Plains=lotsa grass=high equine population. So the Clovis people would evolve with many horses and oxen about them. I have circled the area in gold. The horses would fan-out from there, eventually maing its way to the banks of the Rio Grande, go both east and west, and after a very long time probably make it to the Andean highlands. However, those equines in high areas (Rocky Mountains, Andes) would be smaller, so perhaps horses wouldn't take very well there.
So the way I see it, the Clovis, Messisippian, and whatever cultures border the Great Lakes and Hudson river would become predominant in North America. Then we have to consider what happens post glacier-melt...