High rock walls close in like red- and cream-tinted curtains as a small flotilla of rafts eases into Boquillas Canyon on the eastern edge of Big Bend National Park.

I’m perched on the side of a rugged inflatable boat riding the slow-moving water of the Rio Grande during a three-day trip led by Far Flung Outdoor Center in Terlingua. My toes dangle languidly in water the color of café au lait as a backdrop of knobby rock formations scrolls past. I tip my straw hat back and soak it all in.

This excursion marks the 50th anniversary of the Wild and Scenic Rivers Act, which keeps more than 12,700 miles of river around the country with “outstanding natural, cultural and recreational value” free flowing and open for trips like this one. A 191-mile ribbon of the Rio Grande earned the designation in 1978, and we’re covering 33 miles of it.

 “(The Wild and Scenic Rivers Act) is one of the monumental stepping stones on the long road to environmental awareness, and something all Americans should know about and be proud of,” Tom Vandenberg, chief of interpretive and business services at Big Bend National Park, tells me the next morning as our group of a dozen or so gathers on folding chairs set up along the bank, sipping coffee and tossing back breakfast tacos. “This is what America is — it’s not shopping malls, Whataburgers and Costcos. ... It’s so easy these days for people to forget that.”

The act, he says, protects a vestige of wild America.

Roughly 450,000 people visit Big Bend National Park each year, but relatively few see this thin silvery slice of it. Riding an oar-powered raft through it under normal flow conditions isn’t so much a thrilling roller coaster ride as a laid-back float that gives you time to contemplate your surroundings. Birds wheel overhead, the sun blazes down and, if you’re lucky, a wild horse ambles past.

It’s also a down-and-dirty adventure, complete with mud that sucks off river sandals and sand that creeps its way inside every tent. Don’t come if you don’t like silt-smeared shins, mosquito bites and doing your business in a metal box that’s set up discretely behind the bushes each night.

I feel grateful for the experience. I’ll take sleeping in a tent in the least populated corner of Texas over high thread-count sheets any night.

Our group launched at Rio Grande Village inside the national park and will finish outside its boundaries at a private piece of land near the abandoned community of LaLinda. In between we’ll pause for a hike in a side canyon, swim in the river, stare up at an impossibly star-spangled sky and eat steaks grilled up by our guides on a portable stove.

“The river itself is the unknown corner of the park. People really overlook it,” Vandenberg says. “They know about the canyons, but a tiny percentage of visitors float the river.”

We all shake our heads solemnly. We know it doesn’t get any better than this when it comes to exploring Big Bend. A Rio Grande trip is something that every card-carrying Texan (and those who got here as fast as they could, as the saying goes) should put on his or her list.

“This is as far away from everything as you can just about get,” Vandenberg says. “It’s a vanishing world. The fact that you can come down canyons like this — it’s quiet, pitch dark at night and you’re in this chasm — you just wish everybody had a chance to experience it.”

The Wild and Scenic Rivers Act was put in place to help ensure that future generations can, he says.

As the sun breaches the canyon walls, temperatures quickly warm up, and one by one we wade into the muddy water to cool off before we push off again.

At times, I’m nearly lulled to sleep by the steady plop-splash sound of the oars. But Kevin Urbanczyk, a professor and director of Rio Grande Research Center at Sul Ross State University in Alpine, has work to do. He’s paddling his own canoe alongside our rafts for fun, but he’s also checking instruments along the river that measure its health.

The Rio Grande, downstream of where we are, is considered ecologically sound because of fresh water spring flow. But where we’re rafting, and farther upstream, water quality isn’t quite as good.

“The park’s reach is compromised because of sediment, decreased flow and declining water quality,” Urbanczyk tells us.

Salt cedar was introduced in the 1940s to control erosion, but took over, holding once shifting banks in place and creating gravel bars that choke the river’s flow. Invasive cane, which probably arrived via packing materials, has flourished too, narrowing the river’s channel and holding back sediment that nature once allowed to pass downstream.

Urbanczyk and other researchers hope to find ways to control the invasive plants and improve the river’s health.

Three days after we start, the giant rock curtains that had surrounded the river during our trip open back up. We’ve passed just one other group of paddlers during the entire trip.

“There’s 13 of us here, and at times it feels like I’m the only person out here,” says fellow passenger Gene Fisseler, who is just wrapping up a term on the board of directors of the Big Bend Conservancy, a nonprofit organization that raises funds to help maintain and enhance the national park. “It’s like I’m the first to stumble over this rock or that formation.”

With the empty buildings of LaLinda in sight, the guides pull our boats ashore with a crunch of gravel. Then everyone pitches in to unload gear and lug the boats uphill to a trailer.

I turn around to give the river one last look before we drive away. I remember how the canyon had closed in like theater curtains when we started our tour. The show has ended, I can’t help but thinking, but now I’m ready for an encore.

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