Javelina Formation, Late Cretaceous geological formation in Big Bend National Park, Texas, United States.

The Javelina Formation is a geological sequence of sandstone and mudstone layers found in Big Bend National Park in Texas. The layers show alternating shades of purple and gray that stand out clearly against the surrounding desert landscape and are visible across wide sections of the park.

The Javelina Formation was laid down in the Late Cretaceous, around 69 million years ago, when this part of Texas was a broad river valley. The formation marks the final chapter of the age of dinosaurs, as the deposits end just before their disappearance.

The formation's name comes from the javelina, the collared peccary that still lives in Big Bend National Park. The unit is also known for its paleosol horizons, ancient soil layers that give the rock its banded purple and gray appearance. Spanish-speaking geologists call it the Formación Javelina, and it is correlated with the nearby El Picacho Formation.

The formation can be reached by driving the park roads and walking the hiking trails that pass through Big Bend National Park, where outcrops appear at several spots along the way. Carrying plenty of water and wearing sturdy shoes is strongly advisable, as the ground is dry, rocky, and exposed to direct sun.

The formation's purple and gray bands come from ancient soil horizons, called paleosols, that formed on a river floodplain. The contact with the underlying Aguja Formation is hard to trace in the field, which has caused confusion among geologists mapping the boundary.