“...There were in times past some small thunderegg beds located in the area of Steins Pillar. I believe that any mines are now on private land with no collecting allowed. The eggs from this area have a unique purple tint to the matrix which makes them very distinctive and easy to identify. The agate cores can have carnelian, moss and tubes, with waterline and fortification banding...”

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