Oregon thunder eggs: where to find Oregon’s state rock
Updated . Rules come from Oregon State Parks and the BLM; sources are at the end of the page.
Thundereggs are plain, knobby nodules with an agate core, and Oregon’s state rock since 1965. Fewer places let you dig them than a few years ago: Richardson’s Rock Ranch has closed its digging for good, and the one public site we could verify is Succor Creek State Natural Area, which allows limited souvenir collecting.
- What it is
- A nodule with a knobby rind and a core of agate, chalcedony or quartz
- Where they occur
- Mainly Crook, Jefferson, Malheur, Wasco and Wheeler counties
- Public site we verified
- Succor Creek State Natural Area, Oregon State Parks
- Limit there
- 1 gallon per person a day, 3 gallons a year
Succor Creek State Natural Area is at 43.4665467, -117.1343209. Open in Apple Maps or Google Maps.
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What a thunderegg is
Thundereggs range from less than an inch to over four feet across, but most are about the size of a baseball. They have a knobby rind of drab, silica-rich rock around a cavity filled with agate, chalcedony or quartz. Plain on the outside, they show bright patterns when cut and polished, according to Oregon’s geology agency, DOGAMI.
They always form in silica-rich volcanic rock such as welded tuff and rhyolite. Strictly speaking, a thunderegg is not a rock at all but a structure inside one, as a 1965 DOGAMI study put it. The Legislature made the thunderegg, spelled as one word, Oregon’s state rock with Senate Joint Resolution 18, which took effect on March 29, 1965.
Thunderegg or geode?
The same 1965 study draws the line this way: thundereggs are found only in volcanic areas, unlike geodes and nodules in sedimentary rocks, and they are closely tied to spherulites that formed as volcanic glass crystallized. DOGAMI’s own page still lists the thunderegg as a kind of geode, so you will see both words used.
Succor Creek State Natural Area
- What it is: a deep, rocky canyon in Malheur County that Oregon State Parks calls a remote haven for rock hounds.
- Limit: limited souvenir collecting, up to 1 gallon per person per day and no more than 3 gallons per person per year.
- Getting there: a rough 15-mile dirt road from Oregon 201. The road north of the bridge is not safe for vehicles.
- Facilities: a vault toilet and no water.
- Camping: 4 primitive sites on the west side of the creek and 14 on the east side. The park page lists both April–October and year-round camping, so check with Oregon State Parks before you go.
Other places, and what has closed
- Richardson’s Rock Ranch, Madras: all digging is permanently closed. Its rock shop still sells thundereggs from its beds.
- Pay-to-dig: we could not confirm that any pay-to-dig thunderegg site is open in 2026.
- Other free sites: DOGAMI says thundereggs can be collected at fee and free sites in central and southeastern Oregon, and points collectors to the Madras and Prineville chambers of commerce and the BLM Vale District.
- BLM land: BLM’s 2024 guide for Oregon and Washington names no thunderegg area. On BLM land its general rules apply: a reasonable personal amount, hand tools, no digging deeper than four feet.
- Then and now: already in 1965, most surface specimens were gone and collectors had to dig in soil and talus slopes.
How to open a thunderegg
Thundereggs are sawed open and the cut face is polished. The cutting direction matters: cut the right way, the center shows a star shape. According to the 1965 DOGAMI study, an experienced lapidary can tell from the ribs on the outside which cutting plane will show the best pattern.
Save thunder egg spots
The Capyhound app will keep verified spots, their rules and the map on your phone, even with no signal.
Questions
What is a thunderegg?
A round nodule found in volcanic rock, usually about the size of a baseball, with a knobby, drab rind and a core of agate, chalcedony or quartz.
Is a thunderegg the same as a geode?
Not quite. A 1965 study published by Oregon’s geology agency says thundereggs occur only in volcanic rock, unlike geodes and nodules in sedimentary rock, and are tied to spherulites that formed in volcanic glass. People still often call them geodes.
When did the thunderegg become Oregon’s state rock?
In 1965. Senate Joint Resolution 18 made it the state rock, and it took effect on March 29, 1965.
Where are thundereggs found in Oregon?
Mainly in Crook, Jefferson, Malheur, Wasco and Wheeler counties, at fee and free sites in central and southeastern Oregon.
Can you collect thundereggs at Succor Creek State Natural Area?
Yes, a little. Oregon State Parks allows limited souvenir collecting of up to 1 gallon per person per day and no more than 3 gallons per person per year.
Can you still dig your own thundereggs at Richardson’s Rock Ranch?
No. The ranch says all digging is permanently closed, but its shop near Madras still sells thundereggs from its beds.
How do you open a thunderegg?
Saw it open and polish the face. Cutting in the right direction shows a star-shaped center, and an experienced lapidary reads the ribs on the outside to choose the cutting plane.
