I can’t help the impulse. Whenever I’m hiking through the western forests, prairies, and deserts, my mind conjures up images of Ice Age beasts. I guess I keep engaging in the fantasy because I know I just missed them. Ten thousand years is nothing from a geologic perspective. Shasta ground sloths wouldn’t seem out of place shuffling through groves of Joshua trees, mastodons should still be cracking conifer boughs in the woods, and the grasslands were so recently the place where deer, antelope, and camels played.

But the places I scuff my boots aren’t the same as they were back in the heyday of North America’s enormous herbivores. While there have only been a few clicks of the