Petrified Wood

After waxing poetic about the Painted Desert and petroglyphs in Petrified Forest National Park, now it’s finally time to close out our two day adventure with a focus on petrified wood!

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.

Petrified log cross-section close up

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.

Petroglyphs in Petrified Forest National Park

Day 2 in Petrified Forest National Park found us once again on a ranger led hike, with the same rangers as the day before. This time we were on the south side of I-40 in a different part of the park, and the day’s objective was to find petroglyphs and some native pot shards. Our hike the previous day had only one other person, but this hike was full with 16 people plus the guides! Apparently the local Arizona residents get super-excited by petroglyphs and pot shards, so hikes like these are filled months in advance.

After a long hike across fairly flat land, our first stop was to see “Starving Man”…

…and in addition to the Man, the rock was covered with historic “graffiti” from different time periods and in different styles. The area had a number of petroglyph sites with recognizable human figures and faces, animals…

…and all other manner of images. Once we learned to spot them we found them all over the place out there.

In addition to the petroglyphs, we saw some interesting pieces of broken pottery. One lady had a book that showed many of the styles to help identify the century when things were made.

The simpler, everyday type of pottery was like this “corrugated” shard…

…and the fancier kind was painted and decorated. The piece she looked up was probably made in the 13th century. Now I understand why these kinds of hikes are so popular!

After a much-needed pause for lunch, we continued our long elliptical path around Martha’s Butte.

We climbed up some bentonite hills to get a better perspective, and the rangers found some petrified wood that had been worked into tools by Native Americans. Even the scattered pieces of petrified wood up there (about 5700′) were bright splashes of color against the soft brown of the ground.

Petrified wood
Petrified wood

Just as with the Painted Desert badlands, the basalt caprock has cracked and crumbled away to reveal the soft bentonite which is easily eroded.

The ravens agree with us – it’s a fantastic place… and yet there’s STILL more that we saw after the long hike… stay tuned.

Exploring Arizona’s Painted Desert

As I mentioned in the last post that although we were gobsmacked at the beauty of the Painted Desert (we were in the section that’s in part of Petrified Forest National Park), we took things to the next level by joining some rangers for a hike down into the badlands. Just to refresh your memories, here is what it looks like from the rim at around 5700’…

…and here we go, dropping down into the washes between the bentonite hills.

Bentonite is a generic term for these fine-grained eroded hills, composed of different minerals which give them a variety of colors. The thing that’s important to remember about walking on bentonite is that when it gets wet, it turns to snot! There is no nicer term I can think of to describe the consistency, but it’s slippery, heavy, and clingy… and we would not want to try this in the rain!

Among the bentonite and scrub brush, we also found lots of beautiful mica-like gypsum.

You’re not allowed to collect any rocks or petrified wood in the national park, and we obeyed the rules… but of all the neat rocks we saw I found gypsum (which came in different colors) was the most tempting.

As we meandered around the badlands the rangers showed us a surprise – a hidden pond in the desert!

As the pond was drying at the edges the mud cracked and took on strange patterns.

At one time this whole area (elevation 5400′) was covered by fresh water, and we found plenty of evidence in the form of small shells from freshwater organisms.

And the inundation is what caused the wood in this area to petrify. Petrification starts when an organic material is saturated with dissolved minerals, and the minerals in this area came from volcanic ash. The process takes a very loooooong time as you can imagine, and eventually the minerals replace the original material (with few more steps and lots more time) and then: ta da! You have petrified wood.

Petrified wood

In this part of Petrified Forest National Park a lot of the petrified wood is a dark color, which indicates the presence of magnesium. As you’ll see in the next post, the petrified wood in the southern part of the park displays more and brighter colors. Where the wood started to decompose before petrification began, crystals formed in the voids creating beautiful sparkles.

We thoroughly enjoyed our hike and the company of the ranger couple who led it – they shared a wealth of information and made this first day of our visit really special.

Caverns, Tombstone and the Painted Desert

We spent a day visiting Arizona’s Kartchner Caverns State Park – which was pretty interesting, but they absolutely do not allow cameras in the caverns… which, for me, is almost a deal-breaker. For $120 they offer occasional opportunities for photographers, but I didn’t need pictures of stalactites that badly… so you’ll just have to use your imagination and the link above to see what it’s all about. Discovered in 1974 by two cavers, they spent quite a few years working with the land owners and the state to establish adequate protection for the caverns so they wouldn’t be spoiled by vandals or thieves. It’s now a pristine state park for all to enjoy, and they have taken GREAT pains to preserve these beautiful caverns. Measures included several “air lock” type doors to protect the cavern’s high humidity from the arid desert air. Visitors walk under a light water mist as they enter, and walkways have high curbs – all to minimize the introduction of lint from people’s clothing. Apparently, lint can provide food for undesirable microbes in a cavern system, and it’s the #1 problem for show caves. The place is well worth a visit.

The next day Jim wanted to check out the town of Tombstone, which was largely (as I feared) touristy and ticky-tacky. Tombstone was founded in the late 1800s when a prospector found some silver ore, resulting in the rapid expansion of the town.

The famous shoot-out at the OK Corral happened here, and for a fee you can see it re-enacted (we passed).

The museum in the old County Courthouse was pretty interesting, and the tour into one of the silver mines was fun.

It was time to move on, and we headed northeast to Petrified Forest National Park and the Painted Desert, bisected by historic Route 66 and Interstate 40. The Painted Desert is a vast area, and only a small part of it is within Petrified Forest NP.

Painted Desert is just gorgeous – badlands composed of crumbly rock layers that have been eroded once their capstone of basalt crumbled. Various minerals give the bentonite hills their different colors.


The park has preserved the Painted Desert Inn along the rim road – it was once a roadhouse that provided dining and lodging for people traveling on Route 66.

Painted Desert Inn

Of course I spotted the display showing the various local plants and minerals that the native people used to dye wool…

But the absolute highlight of our time in the Painted Desert was a ranger-guided hike down into those badlands…

…the subject of tomorrow’s post.