North Dakota State Fossil - Teredo Petrified Wood
During the Paleocene period (approximately 60 million years ago) parts of North Dakota were covered by warm water swamps, similar to Florida today. Sequoias and other trees growing in these swamps fell into the water and were washed out to sea become driftwood. This driftwood was then bored into by the marine shipworms. Under the right conditions this driftwood would become fossilized and replaced with silica through the process of permineralization.
Teredo petrified wood is a common fossil in the Cannonball formation which outcrops in Morton County, North Dakota.
Petrified wood is also the state fossil of Louisiana, Arizona and state stones of Texas and Washington.