The Vanished Rivers Beneath Your Feet

You're moving through classic Mesa Verde country here, at just under seven thousand feet, where the landscape opens up in that characteristic stair-step pattern. These are the sandstone benches and slopes of the Mancos Shale, capped by the harder Dakota Sandstone, and if you look carefully at the mesa walls around you, you'll see they're not solid at all. They're riddled with holes, alcoves, and shadowy recesses that hint at something extraordinary happening beneath the surface.

What you're looking at is the northwestern edge of the Colorado Plateau, where rocks laid down in ancient seas about ninety million years ago are now being slowly dissolved from the inside out. The Dakota Sandstone and underlying Entrada formations contain beds of gypsum and limestone, both highly soluble rocks. When slightly acidic groundwater seeps through fractures in the overlying sandstone, it begins eating away at these softer layers, creating a hidden network of cavities and passages.

This isn't full-blown karst terrain like Kentucky or Slovenia, but it's what we call pseudokarst, caves formed in sandstone rather than pure limestone. The alcoves you see in these canyon walls often connect to deeper chambers behind them. Many of the Ancestral Puebloan cliff dwellings around here were built in alcoves that were originally formed by this dissolution process, later enlarged by a phenomenon called spring sapping, where groundwater seeps out along rock layers and undermines the cliff face.

Now here's the dramatic part. During wetter periods of the Pleistocene, maybe fifteen thousand years ago, this region received twice the rainfall it does today. Underground rivers carved extensive cave systems through these formations. Then the climate shifted. As it dried out, those underground streams vanished, leaving behind empty tunnels and chambers. The caves began to collapse in places, creating the alcoves and natural bridges you see today. Some passages are still intact, hidden behind rockfall or narrow openings.

Right now, beneath this seemingly solid landscape, there's a ghost of an ancient drainage system, a network of dry passages where water once flowed in complete darkness through stone. Every alcove, every shelter, every mysterious recess in these canyon walls is a window into that lost underworld. Keep your eyes on those cliff faces ahead.