Big Bend Ranch State Park, Texas state park and International Dark Sky Park in Brewster and Presidio Counties, United States.

Big Bend Ranch State Park is a sprawling preserve across 311,000 acres of desert landscape with mountains, canyons, and roughly 37 miles along the Rio Grande riverbank. The terrain features rugged mountain formations and open plains that extend across the border region between Texas and Mexico.

Native American rock art shows thousands of years of indigenous presence. In the early-to-mid 1900s various owners consolidated the land into a working ranch. Businessman Robert O. Anderson offered it for sale in 1986, and the Texas Parks and Wildlife Commission bought the ranch in 1988 for $8.8 million, with Andrew Sansom leading the acquisition. It opened as a state natural area in 1991, became a state park in 1995 and fully opened in 2007.

The park keeps a herd of longhorn cattle under open-range management, and a roundup is held twice a year. Native American rock art sites in the park record thousands of years of indigenous presence. The name Big Bend refers to the great curve of the Rio Grande along which the park lies.

Access is via FM 170 along the Rio Grande or a Texas Parks and Wildlife airstrip; the headquarters is at the Barton Warnock Visitor Center in Lajitas. Only primitive campsites exist, and the park was expected to draw about 2,500 visitors in 2008. Colorado Canyon is the most accessible river canyon, reachable from vehicle access points and short float trips.

Madrid Falls, Texas's second-highest waterfall, drops through the Bofecillos Mountains; its rough approach keeps most visitors away. Colorado Canyon, cut from volcanic rather than limestone rock, is the park's most accessible river canyon and supports yuccas and cacti on its mineral-rich walls.