Richardson’s Rock Ranch

Come for the rock, not the shovel. Richardson's says it plainly on its own site: all digging is permanently closed. For generations this was the thunderegg dig, the one rockhounds planned a summer around, and it is not that any more. What is still here is the rock shop, and it is not a consolation prize: they sell eggs freshly dug from their own beds, including the famous Priday Agate Beds, cut and polished so you can see what is inside before you buy. The Priday plume bed is the one people come for, red and yellow plumes suspended in a clear matrix. The ranch has been family-owned since it opened in 1974.

Hours are seasonal. From May to September it is nine until five, Thursday through Tuesday, shut on Wednesdays. From October to April it is nine until four, Friday through Tuesday, shut Wednesdays and Thursdays. It is at 6683 NE Hay Creek Road outside Madras, in Jefferson County.

What a thunderegg actually is explains why this ground is worth anything. They form in rhyolitic volcanic rock, where water percolating through the porous rock carries silica in solution and lines a cavity, first with a darker matrix and then with an inner core of agate or chalcedony. Later layers can be agate, jasper or opal, singly or together, and quartz and gypsum crystals turn up inside as well. The colours come from whatever minerals the water passed through on the way in, which is why one bed produces plume and the next produces something else entirely.

From the outside they are dull, rough spheres, usually about the size of a baseball, though they run from a little over a centimetre to more than a metre across. The whole appeal is the gap between that plain shell and the pattern inside it, which is only revealed by cutting.

Oregon made the thunderegg its state rock on 29 March 1965, after a push by the Springfield Thunderegg Rock Club. The largest deposits in the state are in five counties, Crook, Jefferson, Malheur, Wasco and Wheeler, and Jefferson County is where you are standing. The name comes from local lore that the stones were the eggs of thunderbirds living on Mount Hood and Mount Jefferson, hurled at one another by Thunder Spirits.