Many parts of FM 170, The River Road, are actually some distance from the Rio Grande, separated by hills and rocky ridges - such is the case for a 12 mile stretch about one third of the way from Lajitas to Presidio. At one point the road is less than a mile from the river, which is hidden from view behind a cliff face and a plateau several hundred feet high, but a seasonal stream flowing from the desert land beyond has cut a narrow canyon right through, just 3-4 meters wide and with sheer, vertical walls. This is Closed Canyon, one of the best features in Big Bend Ranch State Park, and one which is very easy to explore - the entrance is just a few minutes walk from the road and there are no major obstacles until near the end, when there are several vertical drops in the canyon floor.
The Canyon: The rock is igneous in origin and dark in color, though worn smooth and whitish grey by the occasional floods that rush down the streamway. The ravine is rather different to the sandstone slot canyons of Arizona and Utah, not as narrow and with more subtle patterns of erosion, but with some features in common such as plunge pools and dryfalls. Doubtless the flash flood danger is just as real, and here there are no escape routes once past the entrance.
Rocks: Closed Canyon is signposted from the road, and reached by walking down the stony streambed that leads to its opening. One inside, the temperature drops noticeably and the walls close in abruptly. The course is generally straight with small bends every 50 yards or so. The floor is mostly smooth, bare rock, with only occasional sand banks, bushes or patches of pebbles. The cliffs above are old, dark and weathered; the rocks are sedimentary in origin but seem metamorphosed by time and the harsh climate.
Obstacles: The canyon is generally quite level but has some downward steps of a few feet - these increase in height towards the river. Several have pools beyond, with water that may be 2-3 feet deep. Not far above the confluence, the streambed drops by 10 feet and a rope is needed to continue; an iron peg is driven into the rocks as a belay point to assist when climbing down. This dryfall is about 20 minutes walk from the road.
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