A cut and polished matching pair of thunderegg agate.The Richardson Recreational Ranch, located northeast of Madras in Jefferson County, Oregon, was originally established as a cattle ranch with roots dating back to the late nineteenth century. In 1974, the Richardson family officially expanded into the rock business, opening a dedicated rock shop that eventually grew into a world-famous destination for rockhounds. The geology of the 17,000-acre property is defined by the John Day Basin, featuring extensive rhyolite lava flows and volcanic ash deposits dating back to the Eocene epoch, roughly 35 to 40 million years ago. These soft, decomposing volcanic matrices host some of the most concentrated and diverse deposits of spherical nodules in the region, including the legendary Priday Agate Beds which the family acquired in 1976. While the ranch ceased its famous public fee-digging operations in 2019, it continues to operate its commercial rock shop using stockpiled and newly excavated material.Thundereggs, which became Oregon's official state rock in 1965, are spherical, nodular geode-like rocks that form specifically within rhyolite lava flows. During volcanic eruptions, gas pockets and steam bubbles trapped within the cooling lava created hollow chambers. Over millions of years, silica-rich groundwater percolated through the porous volcanic rock, slowly depositing layers of chalcedony, agate, jasper, or macrocrystalline quartz inside these cavities. While the drab, bumpy exterior of a thunderegg resembles ordinary mud or basalt, cutting the nodule in half reveals colorful, starry, or banded patterns unique to each specimen. The name itself stems from regional Native American legend, which held that the round stones were weapons hurled by the angry thunder spirits dwelling on Mount Hood and Mount Jefferson.
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