We don’t think the Grand Canyon existed six million years ago. But squirrels existed, including the Abert’s squirrel, which was named, of course, after some guy named Abert. Then the canyon popped into place, thank to the Colorado River flowing and the land moving around. After a few million years, some squirrels found themselves north of the canyon, while others found themselves south.

The south squirrels are the Abert squirrel and have a wide presence in the world, including in Mexico and in the Southwest of the U.S. The north squirrels, however, became their own species. They’re called Kaibab squirrels because they’re stuck on that bit north of the canyon, the Kaibab plateau.

It can’t move north because the north is the desert. It can’t move south because the south is the canyon — and while it can physically descend that way easily enough, the climate in the canyon is just as inhospitable for this narrowly evolved squirrel as the desert is.

So, it’s trapped there. Luckily, it doesn’t want to go anywhere else, as far as we know. The Kaibab plateau has all the acorns and fruit it wants.