Much of Petrified Forest National Park is a glimpse of the Triassic, which occurred about 225-207 million years ago. At that time, this part of Arizona sat at the southwestern edge of the Pangaea supercontinent just north of the equator. The climate was the opposite of today – subtropical, humid and plenty of rainfall. Mountains to the south and southeast flanked a low plain, which is where the national park now sits, with a sea to the west.
As streams flowed across this low plain, they covered it with sediment. Sometimes fallen trees, dead animals, and other plants were buried in the mud, silt and clay then later fossilized. Today, this snapshot of the early days of the dinosaurs is called the Chinle Formation.
Much of the formation remained buried under sandstone for eons. Whatever was laid down upon it during the next 200 million years – the Jurassic, the Cretaceous, and much of the Tertiary – has eroded away over time.
Around 60 million years ago, tectonic movement caused a vast area, now known as the Colorado Plateau, to rise to an average elevation of about a mile or so above sea level. The national Park sits on this plateau. Then some 4 to 8 million years ago, sediments buried the Chinle in a layer called the Bidahochi Formation. The Bidahochi formed when a large lake basin covering northeastern Arizona laid down silt, sand and clay with ash from volcanoes in southwestern Nevada.
During the past 2.6 million years, windblown sand covered the Bidahochi. Grass and other vegetation has stabilized some of the sand dunes.
As the dunes and the Bidahochi erode away, it has revealed the Chinle. Wind, rain and the freezing-thawing cycle has shaped the Chinle into a badlands of multi-colored buttes known as the Painted Desert.
Here are some great trails to explore the national park’s fascinating geology.
Painted Desert Rim Trail
This 1.2-mile round trip trail offers day hikers stunning views of a vibrant badlands. It stretches from Tawa Point to Kachina Point on the park’s northern side. The trail showcases an expansive badlands composed of red and white rock formations, shaped over millions of years by water, wind, and the natural freezing and thawing process. These sedimentary rocks were deposited around 200-230 million years ago during the Triassic period, with red sand being trapped by white volcanic ash and gradually transforming into stone. Hike this trail between September and May to avoid the intense summer heat.
Devil’s Playground Loop
The Devil’s Playground Loop spans 7.5 miles in a secluded part of the national park. It boasts hoodoos and enchanting rock formations shaped by erosion and adorned in blue, purple, and gray hues. The trail commences beyond the Lithodendron Wash, adjacent to two brown NPS signs, offering a well-marked path with a few areas near the hoodoos for exploration, and a dry falls on the northwest side. Access to this area requires a wilderness permit and some bushwhacking to reach the trailhead.
The Tepees
The Tepees are distinctive conical hills made of banded mudstones, resembling tepees or tipis. The Tepees are a notable feature of the Blue Mesa Member, which belongs to the Chinle Formation. This formation, deposited mor than 200 million years ago during the Late Triassic Period, is best exposed in the Tepees area and includes the Newspaper Rock Sandstone and the Mesa Redondo Member, composed of dark red siltstones and sandy conglomerates. The Chinle Formation contains bentonite clay, a primary component that swells when moist and contracts when dry, resulting in surface movement that hinders plant growth and accelerates weathering. This weathering process gives rise to the formation of rounded mudstone hills. While there is no designated trail to the Tepees, two pull offs along Petrified Forest Road provide opportunities to walk a short distance and capture stunning photographs.
Blue Forest Trail
Spanning 2.4 miles, the trail is located south of the Teepees with a parking area on the east side of Petrified Forest Road. The hike follows an old road to reach the Blue Mesa buttes. The Blue Mesa is a distinctive formation characterized by vibrant blue and purple hues, attributed to the mineral-rich sedimentary rocks in the vicinity. These colorful bands of mudstone and sandstone were deposited during the Triassic period, when the region was part of a tropical floodplain. The presence of iron and manganese compounds in the fine-grained rock layers gives rise to the diverse colors seen in the formation.
Blue Mesa Trail
Visitors can day hike through an otherworldly badlands of blue and gray banded rock on the Blue Mesa Trail. The 1-mile route is mostly paved and unlike its predecessor – the now Historic Blue Mesa Trail – takes you directly into the badlands. Along the way are fossil-filled rock formations, petrified logs, and even the wildlife that thrives in this alien-like desert. The trail drops into the badlands of bluish bentonite clay set down in the Late Triassic, around 224 million to 219 million years ago. In some spots, the sediment stretches 1000 feet deep.
Billings Gap Overlook
The 234-million-year-old Blue Mesa Member consists of thick deposits of gray, blue, purple, and green mudstones and minor sandstone beds, the most prominent of which is the Newspaper Rock Bed. A 2.2-mile trail allows you to see the Billings Gap, a major wash between two buttes in the Blue Mesa Member. This geological formation is best exposed in the Tepees area of the park. Park at the third turnout on Blue Mesa Scenic Road. The trail heads southeast from the lot alongside Blue Mesa Buttes.
Old Jasper Forest Road
Day hikers can look for desert fauna amid badlands and petrified logs on the Old Jasper Forest Road. The 3-mile round trip follows the remains of an old park road that was popular when built in the 1930s. A badlands area with plenty of petrified wood, the Jasper Forest originally was called the “First Forest” because it was the first spot where railroad travelers encountered petrified logs during the early 1900s. Famous naturalist John Muir was among those travelers, visiting the Jasper Forest in 1905.
Crystal Forest Trail
Day hikers can see thousands of petrified logs – the remnant of an ancient dinosaur-era woodlands – on the Crystal Forest Trail. The 0.9-mile lollipop trail sits in the park’s southern section. Morning or late afternoon mark a good time to hike the trail, as the sunlight’s angle will bring out the colors in the petrified logs. The trail gradually ascends for a fairly good vista of the badlands with petrified logs and the rolling grasslands below.
Great Logs Trail
Families can hike the remains of a woodlands dating from the dinosaurs’ earliest days on the Great Logs Trail. The fairly easy walk consists of two loops that combine for a 0.6-mile round trip. Some 225 million years ago during the late Triassic, the petrified logs along the trail were part of a large forest that covered this part of the world. Nine different kinds of trees – all of which are extinct – as well as ferns and more than 200 other plant species were fossilized when floods washed them into riverways. Sediment and volcanic ash covered the fallen plants before they could decompose.
Long Logs Trail
Hikers can see petrified trunks of nearly quarter-of-a-billion-year-old trees. Petrified logs appear off the side of the trail, looking like tree stumps in the desert brush. Some 218 million years ago, flood waters drove fallen trees – some of them 200 feet high – downstream. The tree trunks piled up in a log jam where they later were covered by silt and petrified. All of these eons later, erosion has exposed the now stone trees. The trial sits off the main park road.
Learn about other great national park day hiking trails in my Best Sights to See at America’s National Parks guidebook.
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