On the inside, however, the thunderegg can be filled with intricately laced formations consisting of agate ... are mainly located in central and southeastern Oregon, including Crook, Jefferson ...

The Polka Dot Agate Mine: The Polka Dot Agate Mine is ... For information on where to dig for thundereggs in central Oregon, contact the Madras Chamber of Commerce at 541-475-2350 or the ...