Welcome to Winslow, Arizona along historic Route 66! In the parking lot of the visitors center, you will find two petrified logs from nearby Petrified Forest National Park. They grew more than 200 million years ago, during the Late Triassic period, and now turned to colorful stone through the process of permineralization.
This EarthCache provides an opportunity to explore the geology, paleobotany, and fossilization processes of petrified wood. Visitors will gain insight into how wood becomes stone, the unique mineralogy of the area, and what these ancient trees tell us about Earth's distant past.
🌲 What is Petrified Wood?
Petrified wood is a type of fossilized plant material where the original organic components of wood have been replaced with minerals, most commonly silica (SiO₂) in the form of quartz, while preserving the tree’s original structure. This fossilization process is called permineralization, which occurs over millions of years.
The wood at Petrified Forest primarily originated from a now-extinct tree related to modern-day conifers, often referred to by its scientific name, Araucarioxylon arizonicum.
⏳ How Did This Happen?
During the Late Triassic (approx. 225 million years ago), this region was a lush, tropical floodplain filled with rivers, forests, and diverse wildlife. When trees died, they often fell into rivers and were quickly buried under sediment rich in volcanic ash. This rapid burial protected the logs from decay and provided the necessary minerals for fossilization.
Over time, groundwater carrying dissolved silica infiltrated the buried logs. This silica gradually replaced the organic wood tissues, cell by cell, crystallizing into quartz. Impurities such as iron, manganese, and carbon gave the petrified wood its brilliant reds, yellows, purples, and blacks.
🧪 The Colors of Petrified Wood
The colors in the petrified logs are not just beautiful—they are chemical clues. Here are the most common colorations and their causes:
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🔴 Red/Orange: Iron oxide (hematite)
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⚫ Black: Carbon or manganese oxides
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🟡 Yellow/Brown: Goethite or limonite
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🟣 Purple/Blue: Trace amounts of manganese or hematite
🌎 Geological Setting
The petrified wood is found primarily in the Chinle Formation, a sedimentary rock unit that preserves an extensive record of Late Triassic ecosystems. The logs are often embedded in mudstone, siltstone, and sandstone, which once formed ancient river channels and floodplains.
This area’s geology also tells the story of plate tectonics, ancient climate shifts, and biological evolution leading up to the rise of dinosaurs.
Works Cited
https://www.nps.gov/pefo/learn/nature/petrified-wood.htm
https://www.nps.gov/pefo/learn/nature/geologicformations.htm
https://www.nps.gov/articles/nps-geodiversity-atlas-petrified-forest-national-park.htm
https://www.journals.uchicago.edu/doi/10.1086/629441
https://home.nps.gov/articles/000/permineralization-and-replacement.htm
https://en.wikipedia.org/wiki/Petrified_Forest_National_Park
https://en.wikipedia.org/wiki/Permineralization
https://www.geocaching.com/geocache/GC205H5
TO LOG A FIND ON THIS CACHE YOU MUST ANSWER ALL THE QUESTIONS BELOW. YOU CAN CONTACT ME THROUGH MY EMAIL OR THE GEOCACHING MESSAGE CENTER TO SEND YOUR ANSWERS. ANY INCORRECT ANSWERS MAY RESULT IN A CLARIFICATION RESPONSE FROM ME.
1. "Petrified in Winslow" on the first line of your email AND list all geocaching names of your party so I can match your answers to them. If you all want to learn something, I would prefer each cacher send me individual emails in the spirt of earthcaching.
2. Take a photo of you (or your signature item if you don't want to show your face) with the petrified wood log in the photo. This photo MUST be uploaded to your "found it" log. Please do not send any photos through the message center as Groundspeak compresses images. Each log MUST have a unique and different photo. No two logs may contain the same photo.
3. Tell me the diameter, height, and overall shape of the logs. Are they rounded or oblong shaped? Why do you think this is the case?
4. Look closely at the texture of the petrified wood. (a) Are growth rings visible? If so, try and estimate the age by counting them. (b) If not, what does this tell you about the tree’s growth environment?
5. (a) Describe the colors you see and (b) based on this, name the two dominate minerals that are present.