The Puzzle of the Pimpled Prairie Persists

Cascade PBS explores the enduring mystery of the Mima Mounds near Olympia, Washington.

Published on Mar. 4, 2026

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Despite two centuries of scientific investigation, the origins of the Mima Mounds, a strange prairie filled with small, evenly spaced hills south of Olympia, Washington, remain a mystery. Cascade PBS's resident historian Knute Berger and co-host Stephen Hegg delve into the various theories that have been proposed over the years, including earthquakes, fires, floods, and ancient gophers, and get insights from local geologist Patrick Pringle.

Why it matters

The Mima Mounds have long fascinated scientists and the public alike, as the origins of these unique geological formations continue to elude explanation. Understanding the formation of the Mounds could provide valuable insights into the region's geological and ecological history.

The details

The Mima Mounds, located south of Olympia, are a series of small, evenly spaced hills that have puzzled researchers for centuries. Various theories have been proposed to explain their formation, including the idea that they were created by ancient gophers, the result of earthquakes or fires, or even the remnants of ancient Native American settlements. However, none of these explanations have been conclusively proven, and the Mounds remain a mystery.

  • The Mima Mounds have been the subject of scientific investigation for over 200 years.
  • Cascade PBS's Mossback video series recently explored the Mounds and the ongoing efforts to unravel their origins.

The players

Knute Berger

Cascade PBS's resident historian who has explored the Mima Mounds and the various theories about their formation.

Stephen Hegg

Co-host of Cascade PBS's Mossback video series, who joined Berger in investigating the Mima Mounds.

Patrick Pringle

A local geologist who provided insights into the Mima Mounds and the ongoing efforts to understand their origins.

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What they’re saying

“Despite two centuries of speculation and science, a strange prairie full of small, evenly spaced hills south of Olympia remains a mystery.”

— Knute Berger, Historian (Cascade PBS)

What’s next

Cascade PBS plans to continue exploring the Mima Mounds and the ongoing scientific efforts to unravel their origins in future episodes of the Mossback video series.

The takeaway

The Mima Mounds remain one of the most intriguing geological puzzles in the Pacific Northwest, captivating scientists and the public alike. As research continues, the hope is that the origins of these unique formations will be finally revealed, providing valuable insights into the region's history and ecology.