AUSTIN (KXAN) — Approximately 80 million years ago, during the age of dinosaurs, the Austin region was submerged underwater with an active volcano rising above the terrain. While the age of dinosaurs is long past us, Pilot Knob remains as an extinct volcano in southeast Austin, described by local geologists as a window into history.

Pilot Knob

  • Pilot Knob, Pilot Knob Acres
  • ~20 min from Austin
  • Hours: Open 24/7

“If I were giving a tour for aliens from another planet that came to Austin and I could make three stops in Austin, I would show him Mount Bonnell, I would show him Barton Springs and I would show him Pilot Knob,” said Chock Woodruff, a geologist with the Bureau of Economic Geology at the University of Texas at Austin.

Nestled in southeast Austin near Austin-Bergstrom International Airport and McKinney Falls State Park, Pilot Knob rises near Cottonmouth Creek. To the untrained eye, it might just look like a stretch of hills.

But beneath the surface was once an active body of magma, the molten material that, under the right circumstances, gave way to volcanic bursts of lava. Without a molten pool still lingering within Pilot Knob, it’s now classified as an extinct volcano as opposed to a dormant one, Woodruff said.

Leon Long, professor emeritus of geology at the University of Texas, holds a volcanic rock sample from the ancient volcano known as Pilot Knob seen in the background in Southeast Austin. (Courtesy: UT Austin / Jackson School of Geosciences)

In its prime, Pilot Knob was active at some point during the Cretaceous Period, roughly 144 million to 66 million years ago, Woodruff said. That period ended with the extinction of the dinosaurs.

During that time, the geographic area now known as Austin would’ve been underwater, operating in marine conditions. Exposed islands would’ve risen up from the sea in regions today known as the Llano and Burnet areas.

“Some of the granite terrain would’ve been exposed, but this would have been a shallow, shallow sea,” Woodruff said.

Pilot Knob would’ve mirrored a tropical island rising above the water levels, surrounded by a reef environment. Volcanic ash material would’ve represented a lagoon, situated between the erupting volcano and reefs surrounding the edge.

Each summer, Woodruff teaches an engineering geology course where students visit Pilot Knob to get a sense of its history. And while he hasn’t given a tour of the site to any aliens yet, it’s one of his favorites to showcase for a new generation of burgeoning geologists.

“It allows them to visualize this ancient geologic feature that you don’t just have everywhere,” he said. “I’m proud of it. I think it’s great.”

This story is part of a KXAN series highlighting Central Texas activities — you can see our full list on our “Central Texas Things to Do” page. Do you have an idea of something we should profile? Email us at reportit@kxan.com.