Wood fiber is replaced by silica (or calcite) to become “petrified”. Submerged in water and buried under volcanic ash (which is loaded with silica), organic tissue buried in sediment decays until the oxygen in the surrounding water is consumed. The decay process releases carbon dioxide, which combines with water to form carbonic acid… making the water around a submerged log slightly acidic. If the water contains silica, the silica will precipitate out and become incorporated into the wood’s cell wall. Voila – petrified wood! The rangers told us that there are examples of petrified wood in all 50 states.
The various colors are produced by different minerals – reds and pinks come from hematite (oxidized iron), yellow, brown and orange come from goethite (another type of iron oxide), green comes from iron (mostly from meteorites), white is pure silica, black comes from organic carbon or pyrite, and purple or blue comes from manganese dioxide. Chemistry surely produces a magnificent palette!
Remember, this is high desert – over 5000′ in altitude. You can see how the caprock crust crumbled leaving softer, almost silty ground layered with mineral colors. As the ground erodes, the petrified logs are uncovered.
As you look around the landscape there are many cone-shaped hills stratified with color. The patterns of the land fascinates with every turn.
We could find petroglyphs at pull-outs along the park road…
…and some unique colors in the Blue Mesa area. Can you spot the people walking on the trail below?
We wanted to go explore down there, but after the long hikes earlier in the day and the previous day we were too tuckered out. It’s okay to leave something to investigate the next time.
Lastly, we stopped to see a little memento of historic Route 66 which runs through the park.