65 million years ago, at the end of the Cretaceous Period, the dinosaurs went extinct. The Paleogene Period (65-23 million years ago) follows this huge extinction with the age of mammals. Big Bend National Park is one of the few places on public land that preserves this transition in the geologic record. This transition, from the Cretaceous (K) to the Paleogene (Pg), is called the K-Pg boundary. Within the park the K-Pg boundary is recorded within the Javelina Formation on the west side of the park and the Black Peaks Formation on the northeast side of the park. Both formations exhibit paleosol (ancient soil) development, giving the sediment a color-striped pattern.
There are three places within the rocks of the park where you can see the K-Pg boundary:
- East-Central Tornillo Flats: The Black Peaks Formation can be seen from the Fossil Discovery Exhibit in the area to the east of the exhibit. Landmarks known as the Black Peaks mark the location of strata laid down during the K-Pg time.
- Western Park Entrance: The Javelina Formation can be seen in the hills between the Big Bend entrance sign and Maverick Entrance Station.
- Glenn Springs Road Wayside (PLANNED): On Glenn Spring Road (4x4, high clearance only), 2.2 miles past the junction with Black Gap Road (~9 miles down Glenn Springs Road), is the location of the wayside that points out the Black Peaks Formation in the creek bed to the southwest. [Note: this wayside exhibit has not yet been installed.]