Rio Grande Wild and Scenic River protects 196 miles of the Rio Grande along the US-Mexico border in far southwest Texas, running from the Coahuila-Chihuahua state line upstream of Mariscal Canyon to the Terrell-Val Verde County line. Designated in 1978, it is the only federally protected Wild and Scenic stretch in Texas - of the roughly 185,000 river miles in the state, only these 196 carry the designation. The NPS administers the unit jointly with Big Bend National Park, which contains roughly 70 miles of the designated corridor. The remaining 126 miles, known collectively as the Lower Canyons, lie outside the park in genuinely remote country where help can be days away. The river here defines the Big Bend of the Rio Grande, where the stream swings northeast after dropping out of the Chihuahuan Desert highlands. It has cut limestone canyon walls that rise as much as 1,500 feet from the water. Inside Big Bend National Park, three named major canyons dominate the paddle-able reaches, each with its own character. Santa Elena Canyon is the most iconic, with 1,500-foot cliffs rising straight out of the water in a fault-block formation that paddlers enter just after crossing into the canyon mouth; the classic Santa Elena run is two to three days with a scramble around the Rockslide rapid. Mariscal Canyon, at the southernmost tip of the big bend, is the most remote of the three and the least paddled, with 1,400-foot walls and two or three Class II rapids depending on level. Boquillas Canyon is the longest, offering two- and three-day floats from the Rio Grande Village area past the village of Boquillas del Carmen on the Mexican side and through a long, steadily walled limestone gorge to a take-out at Heath Canyon near the abandoned bridge at La Linda. Together the three Big Bend canyons offer something close to a full sampler of Chihuahuan Desert river canyon paddling, from half-day runs to multi-day wilderness trips. The Lower Canyons, downstream from Heath Canyon to Dryden Crossing, are considered among the premier wilderness canoe expeditions in North America. The 83-mile trip takes 7 to 10 days and runs Class II-IV with two or three rapids that typically require difficult portages or lining. Riverside springs emerge from the canyon walls providing potable water, and hot springs bubble from the bedrock at several locations. The country is open Chihuahuan Desert - candelilla, ocotillo, lechuguilla, creosote - with bighorn sheep, canyon wrens, burros, and peregrine falcons. Only about 400 people run the Lower Canyons each year. All river use requires NPS backcountry permits. Administration is based at Big Bend's headquarters in Panther Junction.