Richardson’s Rock Ranch — dig Oregon thundereggs

Near Madras, Oregon, Richardson’s Rock Ranch is one of the West’s best-known dig-your-own thunderegg sites. Thundereggs — Oregon’s state rock — are knobby volcanic nodules that hide a core of agate, jasper or common opal. At the ranch you drive out to the beds, dig your own, and pay by the pound.

What is a thunderegg?

A thunderegg forms inside rhyolite lava: a gas pocket is later filled with silica, so a rough, roughly spherical shell surrounds a center of agate, jasper, chalcedony or opal. From the outside they look like plain brown balls; cut and polished, many reveal a striking star- or flower-shaped pattern. Different beds around central Oregon produce their own colors and patterns, including prized plume and moss agate.

How the dig works

At Richardson’s you check in at the rock shop, then head to the marked digging beds to work the loosened ground for thundereggs. It’s family-friendly: much of the material is already broken loose, so even children can fill a bucket. You pay by weight for what you keep, and the on-site shop can cut a specimen so you see the agate inside before you leave. Bring gloves and a bucket; heavier tools help if you want to work fresh ground rather than the turned-over piles.

What you’ll find

The beds & their agate

Part of Richardson’s appeal is that it works several different beds, each with its own personality. Some yield thundereggs with clean blue-gray banded agate, others produce the coveted plume and moss patterns — feathery or mossy mineral inclusions suspended in clear chalcedony — while a few carry common opal or bright jasper cores. Central Oregon as a whole is thunderegg country, the reason Oregon named it the state rock, and the ranch is the easy, legal way to sample that variety in a single visit. Ask at the shop which beds are open and what each is currently producing.

Getting there

The ranch lies north of Madras in central Oregon, off US-97 on a graded ranch road; Madras is about two and a half hours southeast of Portland over the Cascades. Check in at the rock shop first — staff direct you to the open beds and handle the pay-by-weight sorting on your way out. Fuel and supplies are easiest in Madras before you drive out.

When to go

The season runs spring through fall. Central Oregon’s high desert is hot and dry in midsummer, so start early, bring water, sun protection and a bucket, and expect dusty roads. Spring and fall bring milder digging and fewer crowds; confirm the ranch’s open days before you make the drive.

Plan your trip

Pair this with the wider Oregon rockhounding guide and the state’s Glass Butte obsidian beds, and read collecting ethics & the law before you go.

Frequently asked questions

What is a thunderegg?

A rounded nodule formed in rhyolite lava, with a rough shell around a center of agate, jasper, chalcedony or opal. Cut open, many show a star-like pattern.

Can I dig my own at Richardson’s?

Yes — it’s a dig-your-own ranch. You work the marked beds, keep what you find, and pay by the pound at the rock shop.

Is it good for kids and beginners?

Very. Much material is already loosened, so families can fill a bucket easily, and staff will cut a thunderegg to reveal the agate inside.

Why is the thunderegg Oregon’s state rock?

Thundereggs are abundant and celebrated across central Oregon’s old volcanic country, so the state adopted the thunderegg as its official state rock.

When should I go?

Spring through fall. Avoid the hottest midsummer afternoons in the high desert, bring plenty of water, and confirm the ranch’s open days first.

Written by The Field & Stone Editors. Informational only — confirm access, fees and current rules before collecting. Published by KEVALEX Group.