There’s a plaque on a bench on Pinnacle Mountain that commemorates a hiker who reached the summit of Pinnacle some 10,000 times, to which any sane observer must surely respond, “God. Why?” Don’t get me wrong, I love Pinnacle. For that matter, I love the fact that its stubby anthill is crowded with so many types of people on the weekends — no place in the state boasts more human diversity on a Saturday morning. But diversity of the ecological variety? That’s lacking. With West Little Rock’s sprawl lapping around its base, Pinnacle is more of an exceptionally grand city park than it is anything remotely wild. Fortunately, just an hour further down the road, there’s Petit Jean Mountain.

The great wooded mesa of Petit Jean was named Arkansas’s first state park for good reason: Its crinkled topography of myriad streams and rocky ridges is unique, cut from the same geological cloth as the Ouachita Mountains to the south yet standing distinctly apart from them in the river-flattened bottomlands. It’s home to probably the best day hikes in Central Arkansas. And now, thanks to Hendrix biology professor Matt Moran, we have a single guide to the trails that crisscross the mountain. The slim, self-published volume (available for $8.99 from is the first comprehensive guidebook to hiking Petit Jean, but it also differentiates itself by emphasizing science as much as it does the contours of the trails themselves.


Moran, who lives on the mountain outside of the park boundaries, strews his book with bits of knowledge about Petit Jean’s animals and plants, its rocks and its history. There are reptiles of the American West that reach the very easternmost limits of their range here: the collared lizard and the western diamondback rattlesnake. The furry, rust-red gunk that clings to the bottom of some creeks turns out to be composed of complex colonies of iron-feeding bacteria. Atop the mountain, look for ripple marks in the sandstone underfoot, the imprint of a river that flowed over the ground millions of years before the first dinosaurs appeared. And shallow canyons along the Seven Hollows Trail contain rare patches of forest that managed to escape both the appetite of timber companies and a major wildfire in 2000.

“This ‘old-growth’ forest is extremely uncommon in Arkansas, where almost all areas have been logged at least one time in the past 150 years,” the guidebook says.


Moran writes like the science professor he is, not John Muir. His explanations are concise and to the point, phrased with the terse precision of an experienced lecturer. The goal of the book seems to be to push the average hiker just a bit beyond a cursory appreciation of a pretty trail. Questions kept popping up as I read: Why are those bacterial colonies found in one stream but not another? Exactly how can the ripples of a river be imprinted in stone, anyway? Why is it the fire in 2000 left some trees unscathed while destroying acres of forest on all sides?

On a recent fall morning, I met Moran at Petit Jean to go for a hike and get some answers. Because it was the first day of gun season, he put me off til 10:30 a.m. in hopes of getting an early morning deer (he got one). Shortly after we set off down the Seven Hollows Trail, he took a brief detour to gently chastise a hiker who was attempting to hack down a sapling for use as a walking stick. Then, it was down into the first canyon, where we followed the banks of a stream matted with red-orange bacteria colonies.


So what’s up with that, I asked? Is it bad for the stream? And why is it here on Petit Jean?

No, he explained, it’s not a bad thing — bacterial mats like this are part of a healthy ecosystem. And the colonies are where they are because of the presence of iron in the stream and the rocks it flows over. This particular bacteria, Acidithiobacillus, is one of the only organisms you’re ever likely to meet that isn’t dependent on sunlight for life.

Plants and algae and other green things live on photosynthesis, a process by which they capture the latent energy of sunbeams — and, of course, animals like us must devour the sunlight harnessed and stored in plants. But bacteria like Acidithiobacillus opt out of this system by using a chemosynthetic process: chemicals in the Earth’s crust, not sunlight, are the source of their food. In this case, it’s iron. Acidithiobacillus harnesses the same chemical reaction that causes iron to oxidize when exposed to oxygen in the atmosphere. In other words, the bacteria is able to capture the energy released by the rusting process itself; its red-orange color is no accident.

I asked more questions until we ran up against the limits of my meager comprehension of chemistry, and we continued up onto a rocky ridge. Underfoot, the stone undulated in a way that looked exactly like the tiny dunes you’ll see rippling beneath the water on a sandy river bottom or beach.


OK, I asked Moran, are these really ripples from a riverbed? How can a ripple be fossilized?

Sandstone is a sedimentary stone, he replied, meaning it’s created as silt and sand are deposited bit by bit and pressure is applied from above. The sludge at the bottom of any river is potential future rock. Sand turns to sandstone as it’s slowly compacted into union by the weight of the water overhead and, later, by the weight of additional layers of new sediment, which is being continually deposited by the river.

But the deposition process isn’t uniform. At some point, a major flood or some similar disruption occurred on this long-vanished river, which flushed a heavy load of sediment onto its bed all at once. Transient ripples of sand were encased in position beneath a new layer of sediment. That sudden dump of new sand also meant it bonded less solidly with the underlying strata, however, which created a layer prone to erosion — and so now, with the sandstone raised into a mountaintop by the intervening millennia, wind and rain chisel out the sandy contours of a 300-million-year-old riverbed.

“Now as the sandstone erodes again, it’s turning back to beach sand. Look,” Moran concluded, stooping down to palm a bit of the substance. We paused there for a few more seconds, fingering the sand.

Down and up we went across the canyons of the trail — despite its name, there are four hollows along the 4.5-mile path, not seven — and noted the contrast between the trees of the highlands and the lowlands. The hollows are filled with large hardwoods (oaks, hickories, sycamore and sweetgum), while upon the ridges the trail snakes through an otherwise impassible tangle of scrubby, adolescent pines. That’s the result of the 2000 fire, Moran said, which thankfully left the hollows mostly untouched.

Why? Because fire has trouble traveling downhill. Leaping flames grasp upward for oxygen, and as fire consumes air it creates updrafts. The fire that hit Petit Jean 14 years ago was an exceptionally bad one, but the flames jumped from ridge to ridge, right over the shallow canyons of the hollows. Fast-growing pines, which tend to be the first trees to return after a wildfire, therefore dominate the highlands.

We reached the final and deepest hollow on the trail, a silent place of hulking gray bluffs and massive trees — a truly mature forest with a thick overarching canopy in shades of yellow and tan. Undergrowth was sparse here.

“There are less than 10,000 acres of real old-growth forest left in Arkansas,” Moran said. (Two hundred years ago, almost all of the state’s 34 million acres was covered in virgin timber.) “Some in the national forests, some down on the lower White River … of course the trees here don’t reach the stature of those, say, in the Pacific Northwest. In Arkansas there’s more extreme weather to wipe out older trees — winds, tornadoes, ice storms. But it’s still pretty impressive.”

We stopped to take it in. “This is my favorite spot in the park,” he said. “It reminds me a little of the Southwest.”


I could see it — the barren rocks towering overhead, the quietness and relative openness of the old forest. There was a touch of a grander, meaner landscape to the trail at that point. With a little imagination, it could almost be an unusually damp corner of a place like Zion National Park, or somewhere in the New Mexico mountains. Really, though, it just felt like the best of Arkansas.