Our
2021 North Dakota Badlands trip was planned mostly to celebrate the release of
the new edition of my North Dakota Hiking Guide (Guidebook), but also to do some
hikes that we didn’t have time for while preparing the guide. One fun hike that
wouldn’t fit in the book is an off trail hike through the Petrified Forest on
the west side of Theodore Roosevelt National Park’s South Unit. Hiking off trail
in the Badlands is not for beginners, the jumbled topography is hard to read on
a map, but we figured our previous experience, and my geology training should
get us through.
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| Fossilized tree stumps. |
The
rocks in Theodore Roosevelt National Park originally were deposited as sediments
during the Paleocene epoch (55-65 million years ago). Rocks of the Bullion
Creek and Sentinel Butte formations are found. These sediments were deposited
by the rivers and streams that drained the ancestral Rocky Mountains. As the
ancient Rocky Mountains began to rise, a chain of volcanoes became active in
what is now Montana and Wyoming. Huge eruptions of these volcanoes sent volcanic
ash as far east as the Dakotas. These ash deposits are found in the park as
beds of bentonite, the clay mineral commonly called gumbo when wet. |
| Jean along the magic mile. |
Petrified
wood is common throughout Theodore Roosevelt National Park. The rapid rate of
Paleocene sedimentation accounts for the formation of fossil wood. In the
Paleocene climate, much of the landscape was covered by thick forests and swamps.
After rapid changes in stream channels or volcanic eruptions, many trees were
buried before they decayed. Following further burial, groundwater began to
circulate through the sediments. Silica that was dissolved from the ash beds
was then redeposited in the wood as groundwater saturated the buried trees.
Eventually, silica replaced and coated much of the woody plant tissues to create
petrified wood. In well-preserved specimens, growth rings and other features still
are visible. The most common type of petrified wood in the park is preserved
tree stumps.
The
Petrified Forest is accessed in two areas along the Petrified Forest Loop. It
doesn’t take much imagination to suspect that the two fossil locales along the
trail connect, and testing this idea would be the goal of our hike. We got an
early start, and still found two cars at the trailhead when we arrived. The
loop is accessed from a short feeder trail where there is often a lone bison
grazing. We decided to try hiking out to the north exposure, then trying to
work our way to the south one.
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| Bison grazing. |
When
we reached the north side of the forest, we left the trail to trace the outer
edge of the forest, hoping to see some different fossils. The fossil bed lies
just below the top of the grasslands on Big Plateau and are exposed by erosion
of two branches of the headwaters of a small unnamed tributary of Wannagan
Creek. We spotted a pair of thin brown
and black layers that appeared to just above the fossil layer and figured if we
could follow the pair, we would be able to trace the fossil layer. |
| The fossil bearing layer. |
Near
the far end of the north exposure is one of the forest’s most magnificent
sites, a long line of huge fossils stretching out away from the trail. We
crossed over the trail and began to follow this line east. The fossils weren’t
much different than what we’d seen along the trail, but some were larger, and
the preservation of features on others was finer. One surprise was that even
without the fossils the area was gorgeous. We poked along the fossil horizon to
the point where we realized that the unnamed branch was getting deep enough
that it might be difficult to cross. So, we left that fossil bed reasoning that
we could discover similar exposures on the other side of the draw. |
| The start of the magic mile. |
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| Detail of the base of a fossilized stump. |
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| View across the fossil forest. |
We
continued over a small butte and into the second draw, still finding prolific
fossils and no sign of other travelers. Continuing along we eventually climbed
back to the grassland elevation and reached the south side of the loop trail,
just east of the end of the fossils. |
| Small butte. |
We
had one other goal for the day, to explore the section of the Mike Auney Trail
on the west side of the Little Missouri River. Our previous efforts to hike
that trail from the east side had been thwarted by high water in the river. We
were able to follow trails to the river, finding the Mike Auney both
surprisingly scenic and in remarkably good shape for what we had imagined was a
major horsepacking route. However, despite cutting through the same layers that
contained the Petrified Forest, we saw no fossils on that trail.We
returned to the south side of the loop trail and enjoyed the Petrified Forest
exposures along the south side of the trail. We seem to do the loop
consistently clockwise, taking much time to appreciate the fossils on the north
side while we are fresh, and hurrying through the south side when we’re tired. |
| Huge fossil in the south side of the loop. |
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| Jean hiking through the south side of the forest. |
By
the end of the day, we were seeing lots of other hikers, the Petrified Forest Loop
likely is the park’s most popular backcountry. We spotted a familiar looking
hiker who asked us if we’d been on the South Achenbach Trail two days ago; it
was the lone backpacker we’d seen on our first day. (South Achenbach Post).
