Jefferson County, Oregon, offers a diverse and geologically rich landscape that has long attracted rockhounds in search of high-quality thundereggs. The county’s volcanic terrain is laced with rhyolitic ash flows that gave rise to nodules containing colorful agate, jasper, and quartz. These thundereggs are known for their intricate internal structures, featuring banding, mossy inclusions, and vivid coloration that makes them ideal for lapidary work and specimen displays.
Among the standout destinations is Richardson Rock Ranch, a popular fee-dig site providing access to multiple beds, each yielding distinctive material. Some beds produce nodules with dramatic, fortification-style agate, while others offer subtle pastel hues or crystal-filled centers. Collectors appreciate the variety and consistency found here, with specimens ranging from small, detailed pieces to large nodules with bold internal patterns. The ease of access and wealth of material continue to make Jefferson County a reliable and rewarding location for thunderegg enthusiasts.