As they say about themselves on their website,
 "A Wonderful Association of Rockhounds"

This is a direct link to the "Northwest Newsletter"
To find a list of rock/mineralogical clubs in Oregon, please go here ...

The following link is to a well researched and factual article about Thundereggs on Wikipedia, with clear photos illustrating thundereggs.  Did you know that thundereggs do not occur only in Oregon, but elsewhere in the world as well?