This image shows a fallen tree, the base closest to the camera, which has been entirely fossilized over millions of years, until it is now completely composed of stone.
The description states:
FAMOUS OLD FAITHFUL LOG
Petrified Forest, near Holbrook Arizona.
–The Petrified Forest is a large area of exposed, fossilized trees in northeast Arizona. These trees were originally buried, allowing them to fossilize, and were exposed by erosion of the surrounding material over millions of years. The national park contains a total area of 170 square miles.
This postcard was used and is dated 13 July 1953.