Agates in Petrified Wood Petrified wood is also associated with agate formation. Agates developed after hollow "paleo" logs were buried by later depositions of sediment. The resulting subsurface voids facilitated agatization with the help of fluid movement, much like the vesicular basalt described above.
Arizona is rich with petrified wood, but it is well regulated, on reservation or private land, or being extracted for its many commercial applications. However, dig for fee sites are available in multiple locations throughout the state. If you haven't already done so, check out our Introduction to Agates page.