Petrified Forest National Park, Day 2

Near Holbrook, Arizona – March 26, 2022

We made our first visit to Petrified Forest National Park on March 25, 2022, restricting our time to only the northern, smaller section of the park. That part doesn’t have much in the way of petrified wood, but it has plenty of awe-inspiring views. We returned the next day, with Gunther, to experience the southern side, and we did see some fossilized wood. And how!

Petrified Forest National Park, which measures about 350 square miles, receives about 600,000 visitors per year. That number, while impressive, makes it just the third-most-visited national park in Arizona, following Saguaro National Park in Tucson (1 million visitors per year; Nancy and I were two of those people a couple of weeks earlier) and the most-visited park in all the land, Grand Canyon National Park (4.5 million). Incidentally, Rocky Mountain National Park in north-central Colorado is just behind Grand Canyon, at 4.4 million visitors per year. If you’ve been to Rocky Mountain National Park in the last 20 years and felt a bit cramped, it’s probably due to 4.4 million other people visiting a park measuring 415 square miles.

Wind and water erosion in the northern Arizona desert does some interesting things to rocks, like resting the one on the right side against the one on the left.

But we’re here to talk about rocks. A piece of petrified wood isn’t really wood any longer: it no longer contains any organic material and it is most definitely a rock. The process of petrification takes several important factors, including a tree, water, sediment, and time. Lots and lots of time.

Many of the rocks at Petrified Forest National Park represent trees that were quite large when they were living, about 220 million years ago. Here we see a park visitor with her dog observing a massive rock. (It’s Nancy, with Gunther, who appears ready to return home to The Goddard but we’d only been at the park for about 30 minutes at this point.)

Let’s start at the beginning. The scientists believe that the trees in Petrified Forest National Park were alive between 210 and 227 million years ago. At that time, the Late Triassic Period, the current area of the park was just north of the equator – in fact, it was close to where Costa Rica is today. The land was much different then: covered with forests of immense trees as well as large rivers and other wetlands. Huge amphibians and early dinosaurs roamed the forests and dwelled in the rivers. (Although there were many dinosaur species in the ensuing years, famous dinosaurs such as Tyrannosaurus rex and Triceratops wouldn’t appear until the Late Cretaceous Period, almost 160 million years later.)

There’s still a lot of detail from the former trees to be seen in their petrified logs. While it appears that the logs have been cut with a chainsaw to achieve those smooth sides, they’ve simply cracked along the crystalline structure of the quartz. That usually happens because of erosional processes: either geologic uplift over millions of years, or supporting materials below the log being removed through relatively quick wind or water action.

Many of these coniferous trees (there are nine species identified in the park; all are now extinct) grew to be enormous: some may have grown to 200 feet in height. When the trees died they lost their branches and bark, then eventually toppled over after being undercut by a river. If the tree fell into the river, it may have eventually been covered in sediment being carried by the waterway. This relatively rapid burial is critical to later petrification: the water sealed the dead tree away from both oxygen and bacteria, which helped prevent decay. That delay gave time for silicic acid in the rivers to percolate throughout the tree. This process chemically altered the wood into a mineral called opal that still retained the tree’s fine features, like the grain of the wood, or indications of where branches once sprouted from the trunk.

This is one of the biggest, if not longest, pieces of fossilized wood in Petrified Forest National Park. “Old Faithful” is 35 feet long and weighs about 44 tons. It’s also one of the relatively few logs that retained part of its root structure, which measures 10 feet across today, during the petrification process. In 1962, lightning struck and fractured this log. The National Park Service used mortar to reattach the pieces and added the retaining wall seen near the base of the former tree – a process that, in the name of resource management, the NPS would probably not undertake today. Old Faithful is located just west of the Rainbow Forest Museum and Visitor Center near the park’s southern entrance.
Here we see a park visitor with her faithful dog, standing next to the base of Old Faithful. (It’s Nancy, again, with Gunther, again; the dog appears to have perked up somewhat.)
While perhaps not quite as spectacular as the views we enjoyed in the northern part of the park the day before, there were still great vistas to enjoy on the Giant Logs Trail near the visitor center. One can see erosional forces still at work on the rocks at right.

Converting the wood into opal took only a few thousand years. Further layers of sedimentation over millions upon millions of years would cover the logs with tons upon tons of soil and rock. This process recrystallized the logs, converting the opal into quartz and a few other minerals. Over many other ensuing millions of years, erosion and geologic upheaval brought the logs back to the surface of the earth to once again see the light of day – this time as petrified wood.

Now that you know the factors involved in creating petrified wood, can you name the states in our country that contain it? The answer is below – keep on scrollin’!

The silicic acid in ancient waterways percolated through fallen logs, converting the trees’ organic material into opal. This closeup photo shows that the minerals retained the features of the trees, such as the grain of the wood.

The visitor center at the southern end of the park, which is part of the original monument created in 1906 (it was made a national park in 1962), contains some interesting fossils of both trees and animals. The fossilized remains of many amphibians and some dinosaurs dating to the time that the trees were alive have been discovered in the park (and the process for creating animal fossils is much the same as that used to create petrified wood). The museum also exhibits some handwritten letters: apparently, some visitors over the years were unable to withstand the temptation (and federal law) to leave the petrified wood where it lay within the park. Upon their return home with a fossilized wood souvenir, some of them inexplicably fell into bad fortune, such as personal or business relationship issues, and returned the rocks via mail, with an apologetic letter, to the national park.

Some of the many trails within the southern part of the park feature these helpful fossilized logs to help keep hikers on the path. Walking beside them gives an idea of just how tall these trees were.

After going to the visitor center and museum, and walking the Giant Logs Trail behind the building, we decided to go on a longer walk to see some more rocks. The Long Logs Trail, located a short distance from the visitor center, is so named because some of the petrified wood is more than 180 feet in length.

We saw this horned lark while on the Long Logs Trail. It had a very pretty song. We had never seen one before, and were happy to watch and listen to it for a while. (I write “we,” but Gunther couldn’t possibly have cared less.)
More than 1,200 archeological sites, indicating prior human habitation as long as 12,000 years ago, have been found in the park. The Native Americans arrived first as nomadic cultures, then over the centuries began to occupy the area on a seasonal basis. Eventually, the cultures lived in what is now the park year-round. A short spur from the Long Logs Trail leads to Agate House, a building that was reconstructed by the NPS to represent an actual seven-room dwelling built by ancient Native Americans, using the only construction material available, petrified wood, about a thousand years ago. Although centuries of weathering caused the original structure to collapse, park service staff used the same rocks to rebuild the house.
Realizing it’s a reconstruction, Agate House is still very pretty and was probably fairly resistant to the elements when it was first built.

About the states that contain petrified wood: were you able to name them? If you named all 50, you’re correct. Although each U.S. state contain some amount of petrified wood, northern Arizona is able to display one of the largest concentrations in the nation because of the geologic upheaval processes that brought the logs to the surface of the earth.

This particular log caught my eye because of the many colors it features. It’s simply spectacular. The different mineral composition within the petrified wood contributes to the varied coloration. The rocks can contain natural quartz, which is nearly clear and translucent, as well as varying amounts of iron, copper, manganese, and chromium, all responsible for the reds, yellows, purples, and greens. I would never take any rocks from Petrified Forest National Park. It would have meant that someone else wouldn’t have been able to see this one. However, if I was going to take a rock home, this would have been the one. But we have a weight limit, for towing safety purposes. on The Goddard. Also, I like my luck the way it is.

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