Washington designated petrified wood as the state gem in 1975 (though rock-hard and beautiful, petrified wood is not actually a gem but a fossil). In prehistoric times, the interior of Washington was swampy with trees such as cypress, oak, elm and gingko. Some of these ancient forests were preserved by lava flows and water and over time became fossilized. You can see petrified wood at Gingko Petrified Forest State Park in Vantage, Washington. Petrified wood is also the state stone of Texas, and the state fossil of North Dakota and Louisiana.