It was clear every nook and cranny had been repeatedly picked over for thundereggs. Little round hollows signifying their absence were everywhere.
“A Thunderegg is not actually a rock. It is a structure, sometimes a nodule, sometimes a geode, occurring in rhyolite, welded tuff, or perlitic rocks. However, without question, the Thunderegg is by far the most popular ‘rock’ in Oregon” (www.naturenw.org/rock-thundereggs.htm).