See the context of this sign.

Boquillas Canyon Trail

To appreciate the canyon's enormous scale, hike to
the entrance where the Rio Grande disappears between
towering cliffs. The 1.4 mile round-trip hike is a journey
down a vast time corridor.

After climbing this low hill, the trail descends to the
riverbank. Continue to river's edge - a scene of utter
remoteness only a few hundred yards from the parking lot.
In rainy season (summer and early fall) the current becomes
cloudy with the grit that endlessly carves the gorge.

In bedrock along the river you might find prehistoric
mortar holes where nomadic tribes ground seeds, roots
and mesquite beans.

On the Texas side, look for the sand dune blown against
the cliff by down-canyon winds.

Don't miss the rest of our virtual tour of Big Bend National Park in 1083 images.