Mineral emplacement in which dissolved minerals are carried by ground water into the porous parts of buried wood, results in petrifaction. We see it in petrified wood, although it is known in shells or bones. Petrified wood made up principally of Araucarioxylon arizonicum may be seen in the Petrified Forest National Park in Arizona. Other sites where petrified wood may be observed is Yellowstone National Park, which is not a single forest but a vertical succession of 27 individual forests preserved in more than 2,000 feet (600 m) of volcanic debris. Not only have the tree trunks been preserved, but the impressions include leaves, twigs, needles, and cones.