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Geologic Snowflake Hunters Flock To Oregon For Thundereggs

Producer - Vince Patton
Videographers - Todd Sonflieth, Nick Fisher
Editor - Nick Fisher, Todd Sonflieth

Prospectors who come to central Oregon typically do not look for shiny flecks in the rock. Instead, 10-year-old Isabelle Anderson and her father Jeff, from Bellingham, Washington, prefer baseball-sized nuggets that are dull, brown, bumpy and round.

“Found one!” she cried as she chipped away at the dirt with a pick and dislodged a perfect candidate: a thunderegg. She actually wasn’t interested in its shell; it’s what the rock has hidden inside that captivates rock hounds.

A "plume" thunderegg features intricate patterns of minerals which virtually mimic floral designs.

A “plume” thunderegg features intricate patterns of minerals which virtually mimic floral designs.

Vince Patton/OPB

Sliced open, thundereggs reveal patterns of colorful minerals encased inside.

What’s amazing is, they don’t know exactly how they’re formed,” says Jeff Anderson. “And when we’re digging here, we’re uncovering earth that’s never been dug up by humans before.”

The Andersons joined hundreds of rock hounds from around the nation who come to Madras each year to dig for thundereggs on local ranches.

These unique geologic snowflakes can hold simple deposits in layers or intricate patterns in greens, golds, reds and purples that can look like floral arrangements of tiny moss or flowers.

Rock hound Bob Rowland says, “Sometimes nature will make something that looks like a scene out of the past. It’ll look like pretty  floral prints. Nature just paints a pretty picture. Nature is the real artist here. We’re just the technicians learning to let it out.”

Oregon lawmakers named the thunderegg as Oregon’s state rock in 1965. The state is recognized as one of the prime spots on the globe to find them. The Richardson Ranch near Madras has made a thriving business out of allowing visitors to buy the thundereggs they dig up on its 6,000 acres.

Rock hounds from around the world dig at Richardson's Ranch near Madras, Oregon, home of the largest thunderegg deposits on the globe.

Rock hounds from around the world dig at Richardson’s Ranch near Madras, Oregon, home of the largest thunderegg deposits on the globe.

Vince Patton /OPB

While thundereggs are not generally found west of the Cascades, one of the region’s largest collections can be found in Hillsboro at the Rice Northwest Museum of Rocks and Minerals.

The museum has nearly 1,000 thundereggs, including a 2-ton version with red and white minerals inside, plus an 800-pound egg called “The Meatball” which has never been opened to show what’s inside.

No one really knows how thundereggs form. However, one theory says a gas bubble forms in the lava, expands as it cools and leaves a hollow hole.

Then over millennia, minerals dissolved in water leak down through the porous stone and fill in the gap layer by colorful layer. 

Other Resources:
Rockhounding on Public Lands

Where to Find Thundereggs
Tips from the Oregon Dept. of Geology & Mineral Industries
All Rockhounds Club

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Part of Episode

Disappearing Frogs Update; Imperial Stock Ranch; Thundereggs (2504)

Oregon Field Guide: Episode #2504
Most Recent Broadcast: October 31, 2013