A photo of Boquillas Canyon.

Boquillas Canyon formed over millions of years as the land steadily rose and the Rio Grande cut downward through the massive escarpment that forms the western flank of the Sierra Del Carmen, a north-to-south trending uplift that extends across the Texas and Mexico border in the eastern Big Bend area. Cretaceous age formations are exposed in the canyon mouth (Boquillas means little mouths in Spanish). From bottom to top, the canyon walls consist of the Del Carmen Limestone (lower cliff), Sue Peaks Formation (shaley slope), and Santa Elena Limestone (upper cliff and slope near ridgeline) (Maxwell, 1986).