Whatever ate this deer, it was really, really hungry. The bones are not just picked clean — they’re gone, most of them, except for about a dozen vertebrae and a few assorted ribs, scattered about in the weeds. “Mountain lion, prolly,” says my guide, Steve Torbit, nudging what’s left of the spinal column. The bones are nice and dried-out, I note with relief, meaning the mountain lion is probably not still nearby.

It had plenty of time to enjoy its venison meal, judging by the way it laid out the carcass on a broad, flat rock beside this stream, the East Fork of Parachute Creek, deep in a fold of Colorado’s spectacular and probably doomed Roan Plateau. We’re only about a dozen miles north of I-70, three hours west of Denver, but it took more than an hour to get here from the highway, bumping along narrow dirt roads that left our Yukon thoroughly scratched, then trudging down a rocky jeep track into this canyon.

“It’s one of those places you don’t accidentally visit,” says, Steve Torbit, Rocky Mountain regional director of the National Wildlife Federation. “You have to mean to get up here.”

Rising 3,500 feet above the Colorado River valley in a series of dramatic shale cliffs, the Roan is a refuge for legendary herds of elk and mule deer, which draw hunters from around the world (some with four legs instead of two, as we’ve seen). The creeks hold rare, pure strains of cutthroat trout that are extinct almost everywhere else in Colorado. “These fish have probably been here for 10,000 years,” said Ken Neubecker, president of Colorado Trout Unlimited, who had tagged along for the ride.

Just downstream from the deer kill, a waterfall spilled 200 feet down into a perfect hanging valley filled with aspen and spruce. Years ago, a friend of mine shot an elk down in a ravine like this. It took him nearly two days to drag it out. “It’s real backcountry up there,” he said. “You feel like you can walk all the way to Wyoming and no...