Wyoming is a state rich in fossil wood and has several petrified forests. The petrified wood from one forest is known to collectors as Eden Valley Petrified Wood and is named after the town of Eden, Wyoming. Eden is located in the west-central part of the state and is in the center of the 80 mile long area where the fossil wood is found. Three collecting areas are well known.

Eden Valley Map

The Blue Forest collecting area is located in the west end of the deposit about 30 miles west of Farson. The fossil wood found in this area is known for the light blue agate surrounding many of the pieces. The Big Sandy Reservoir is located just north of Farson.   This area is known for Petrified Palm Wood. On the eastern end of the deposit, fossil wood is found around Oregon Buttes just east of South Pass, Wyoming.  Oregon Buttes is a major landmark on the Oregon Trail.

Eden Valley Petrified Wood was formed from plants living about 50 million years ago and the rock exhibits features not found in fossil wood anywhere else in the world. The petrifaction process for this area involved shallow "algae growing" lakes. In many cases, for undetermined reasons, the wood came to be in this water in its live condition (see 1st image on the left below) before it had a chance to dry out and look like old dead wood.  This wood became coated with algae (2nd image from the left) which adhered to the surface making a cast or mold around the wood.  Later the wood dried and shrunk in the mold made of algae (3rd image from the left). Over time these algae casts became part of a layered rock formation.   Silica-rich water solutions seeping through the rock then petrified the wood and filled in the spaces left between the dried wood and the hardened cast with agate, calcite, and quartz (4th image from the left). 

As the agate coated the inside surface of the algae cast, perfect impressions of the bark were left in the agate.  Thus there are some rocks that show two 50 million year old "pictures" of the same plant -- one picture of how the plant looked alive and another after it died and dried out!

Because the petrifaction process seems to have been "protected" by the algae cast formation, unusually detailed representations of the wood have been preserved. Exquisite representations of bark both live and dried out have been preserved. Worm holes, insect borings, woodpecker holes, and other events have been observed in the petrified wood.  Even very rare lichen fossils and small clam shells have been duplicated in the agate.

More information may be found in the following back issues of 
Lapidary Journal:
1950    April          Page 16
1953    August      Page 246
1968    May          Page 330
1972    October     Page 1078
1974    May          Page 336