Happy birthday, Big Bend National Park! Since this humongous park was established in Texas in 1944, it has welcomed millions of nature lovers and adventure seekers. The park"s southern boundary is marked by the Rio Grande, which separates Texas and Mexico. If you look at a map, it"s clear how the area got its name. The river has a drastic change in course, bending from southeastern to a northeastern flow around the park"s boundaries.