“... Near to White Rock Springs in the Mill Creek Wilderness is the Sandy Bed claim, which is also closed to collecting, due to being in the wilderness zone. The Sandy bed eggs have a lighter colored matrix than the White Rocks, and the few eggs I have seen from there have light colored agate cores, some are a pale blue and may contain small black dendrites. ..”

extract of the article from Mark Ketsdever, Hillsboro, Oregon, 2007 :”Thunderegg Agates of the Ochoco Mountains, Oregon, USA”