The Rio Grande of Texas become navigable near the town of Presidio, Texas, where the Rio Conchos brings water from the Sierra Madre of Mexico to the river. For about 20 miles, the river flows through the La Junta valley, the oldest continuously cultivated area in the United States. Then, the river cuts through the volcanic mountains to form Colorado Canyon. The numerous riffles and rapids make this 20 mile section of the river popular with whitewater enthusiasts. The resort of Lajitas provides an oasis of civilization before the river begins a 20 mile course through the spectacular scenery of Santa Elena Canyon. The Rock Slide Rapid of Santa Elena Canyon  tops off the adventure before the dramatic exit from the canyon into the brilliance of the desert lowlands.