[Illustration: ARROYO—Arroyos dip below the plains in appalling vistas of sand and desert wasteland revealing the continuous processes of erosion. The foothills of the Chisos Mountains are in the distance.] Outstanding in natural phenomena the scenic features of Big Bend National Park comprise a variety of spectacular attractions. In addition to the canyons of the Rio Grande, numerous colorful arroyos dip below the plains in appalling vistas of sand, rock and scrub vegetation of the desert. Buttresses push their towering masses into the azure sky, revealing a graphic account of endless battles with the elements. The uncovered strata opens the book of geologic history. High in the Chisos Mountains, majestically reigning over the Basin, Casa Grande, an erosive remnant of rhyolite, rises 7,300 feet above sea level. This massive monolith is a conspicuous landmark, photogenic in its moods of shifting lights and shadows. Climaxing the mountain scenery are the outstanding vistas that unfold from the South Rim of the Chisos Mountains. From this lofty plateau, more than 7,000 feet above sea level and a mile above the sprawling valley of the Rio Grande, the extensive awe-inspiring view reaches far into Old Mexico. To the east, blue and purple in the distance, ranges of the Sierra del Carmen and Sierra Fronterisa pose in their grandeur. More than a hundred miles to the south the distant Sierra Madres form the horizon line in Mexico and the Mesa de Anguila forms a sharp outline to the west. Dropping sheer from the South Rim, precipitous cliffs slope into the Lower Chisos, more than 1,000 feet below the rim. [Illustration: TULE MOUNTAIN—Erosion has carved innumerable spires and buttresses out of Big Bend’s igneous rock.] [Illustration: WEST FACE OF THE SOUTH RIM—Dynamic and spectacular, the view from the South Rim of the Chisos Mountains reaches across the Rio Grande and far into Old Mexico.] [Illustration: THE SOUTH RIM OF THE CHISOS MOUNTAINS—Looking west along the face of the South Rim where perpendicular cliffs drop more than 1,000 feet to the lower Chisos. The Rio Grande valley is in the middle distance.] [Illustration: SOUTH RIM VISTA—One of the most spectacular views in Big Bend National Park is the amazing expanse that unfolds from the South Rim of the Chisos Mountains. In the middle distance is the Rio Grande—and Mexico beyond.]