There are large animals that once ranged over large portions of the continent.
I can think of the Bison and the Grizzly Bear as two of them.
Of course they were hunted to extinction over much of their range, so that doesn't apply to Bigfoot. 100,000,000 Bison killed by humans, Grizzly Bear which ranged all the way to Mexico? Killed by humans. Bigfoot ranges from Maine to Arizona, PEI to Alaska, and south to Florida, Texas and Mexico, but no loggers, hunters, or trappers ever got a bead on one.