occur in the Wanapum Basalt Formation (Columbia River Basalt Group) along the Fish Lake Trail, exposed in a railroad cut through the volcanic formation within 100 yards (meters) of one another. One can easily imagine a landscape with a stand of large trees being invaded and enveloped by an advancing lava flow around 15 million years ago. I’m certain that 99% of the trail users aren’t aware of these interesting features and the story they tell.
Note the silicified wood that is preserved near the base of this large tree mold.
This tree mold is about 20 inches (0.5 meters) in diameter.
The underlying paleosol (ancient soil horizon) in which the tree were rooted is clearly seen here beneath the overlying basalt formation. This tree mold is about 15 inches (0.4 meters) in diameter and penetrates the interior of the volcanic unit.