Solitario is a vast geologic structure in Big Bend Ranch State Park in far West Texas whose crater-like form is actually the deeply eroded remnant of a laccolith rather than an impact site. Spanning about 135 square kilometers, it is a structural dome formed in Paleozoic and Cretaceous rocks above an Eocene granite intrusion and includes a volcanic caldera, dikes, sills, tuffs, and lava. Its rocks preserve a long history of folding, uplift, deposition, volcanism, and erosion, making it one of Texas's most remarkable geologic features. The area entered public parkland in 1988 with the creation of Big Bend Ranch State Park.