Wednesday, February 18, 2009

Red Arrow Fault


We took quick, short steps down the steep slope to reach the gaping chasm, part of the park I had never seen before. I had my first lesson in draws and hollows earlier that morning, detailed descriptions of the landscape features I was supposed to use as guides on my hike through the woods. This lesson following, of course, my boss’ perfectly perplexing directions: “Follow that draw ‘til you hit the second holler and go north until you reach the hogback.” I stared at him in disbelief, quiet, stunned that he would think I, having moved from New Orleans to rural Missouri merely two days before, would understand what that sentence meant.

My patient boss, 7 years younger and a lifelong Ozarker, had already given me a cram course in reading landscape features on topographic maps: drainages, cliffs, sinkholes, and steep slopes whose closely knit topo lines look like thick, black Sharpie marks on the page. I came from the flatlands of Louisiana, and translating Ozark features on a map to the rugged landscape itself provided a new challenge. I had never heard of a draw before, a common feature throughout the Ozark Highlands, (a small stream valley formed by erosive downcutting). And despite the visible differences between them on a map, I couldn’t tell the difference between a draw and a hollow (a distinct valley between two hillsides or mountains). All I knew was that I was looking for a deep pool of water where ringed salamanders might breed. Then he throws out “hogback.” I was looking for the hogback located to the north over the draws and hollows, but I had no idea where that was.

I guess my boss could read my blank, unblinking stare that morning in the office. He nodded his head, grabbed his water bottle and bailed into the driver’s side of the filthy white truck, perfectly willing to show me where the salamanders were, willing to essentially hold my hand across the drainages to the rocky hogback. He didn’t say much on our first hike through the pristine Niangua Basin woodlands, a burned landscape punctuated with the first flush of phlox and mayapples, splotches of purple and green on otherwise blackened soils. He was probably wondering why he hired someone who was very likely to get completely lost outside of the narrow streets of an old French settlement. Just the day before, after all, I lost myself in a 4,000 acre prairie while looking for a crawfish in a draw.

Short of breath, unaccustomed to the rugged terrain, I followed him across the hills and valleys, over draws and “hollers.” I see it from yards away: enormous, ragged dolomite and limestone boulders jutting out of the valley, a deep scar on the landscape, a long ridge of boulders that runs a mile long. The geologic feature looks like the stiff bristles on a hog’s back. “Oh! A hogback!” I proudly exclaim to my boss, who slowly shakes his head at the ground. We quickly scamper down the steep slope, dipnet and water quality gear in hand, to peer into the wide, gaping, rainwater-filled chasms produced by the hogback. He was right. The pools of water were filled with ringed salamander larvae.

This jarring feature is rather uncommon to the Niangua Basin landscape, typically a dissected terrain with random dolomite outcrops jutting out of ridgetops. While not part of a hogback’s formal definition, we were actually standing on the sides of a fault line. Called Red Arrow fault, the long row of dolomite boulders is an earthquake feature that rumbles slightly every once in a while. In January 1992, a magnitude 3.1 temblor shook the town of Camdenton when Red Arrow moved; the summer I lived there, the fault line shifted a little on the fourth of July, causing a low rumble heard from town square. Banner headlines followed on the fifth.

One of my favorite lines from Thomas Beveridge’s opinionated and well-researched Geologic Wonders and Curiosities of Missouri reads, “Missouri is well-endowed with faults” (p. 175). While Southeast Missouri Lowlands’ New Madrid Fault garners more press than any other earthquake feature in the state -due in large part to its recent activity- faults are somewhat common features in the Ozark Highlands.

In the Meramec River Hills, the Palmer Fault Zone is a 2 mile wide fault visible from Hwy. 21 outside of Potosi. Rock formations otherwise uncommon in the area are exposed here, noticeable even to the novice geologist. In an area typically dominated by Eminence dolomite and chert, the faulting and subsequent erosion brought LaMotte sandstone and Bonne Terre formations to the surface. The topography around the fault is less rugged than the surrounding area, appearing as gently rolling hills, though the vertical displacement caused by the faulting rises nearly 1,000 feet. Dolomite returns to the surface at the far edge of the fault line, where the jagged terrain associated with the surrounding landscape resumes.

The Ste. Genevieve fault system, located in the Outer Ozark Border near the Mississippi River, is a much larger system, visible even on Landsat imagery from nearly 500 miles above the surface of the earth. This complex fault line causes over 1,000 feet of elevation change and stretches from Perry Co. through Ste. Genevieve Co. and into St. Francois Co. One side of the fault exposes Cambrian rocks, while younger Mississippian rocks can be seen on the opposite side. At Hwy. Z outside of St. Mary’s, I-55 crosses this fault, evident by the crushed, steeply dipping rocks on both sides of the highway.

Most Missouri faults are not closely related to historic earthquake activity. Instead, they provide geologists a glimpse into the earth’s surface, an opportunity to see what rests below the bedrock. Of course, in the case of Red Arrow, the earthquake feature is a great place to find breeding salamanders.

4 comments:

John said...

This post reminds me of how much "hillbilly" I've got in me!

I had a similar experience a few years ago, albeit on the other end of the conversation. While scouting a trail reroute, my partner Robert looked at me with puzzled eyes when I told him to "walk past that line of stobs, head up the draw and cross at the saddle."

He's gotten the hang of stobs and saddles, but he still wants to refer to draws as "reentrants."

Allison Vaughn said...

Reentrant? Wow. If I said that in my circles I'd get punched.

Heber said...

Could you tell us more about the salamanders you were studying on that trip? I have heard that salamanders in the Ozarks are being threatened by feral hogs. Are there numbers in severe decline?

Allison Vaughn said...

You're exactly right, feral hogs are really impacting all of our amphibian and reptile populations, not to mention ground nesting birds and the entire flora of any area where they live. I wrote about feral hogs back in November after I came across a whole mess of them. Right now they're really concentrated in the St Francois Mountains--Taum Sauk, Sam A Baker, Johnson's Shut Ins, lots of Forest Service land-- and around the White River Hills on Forest Service land. Some have been found around Cuivre River. I was actually looking at ringed salamander populations and hogs haven't been a problem in the Niangua. Be careful when you go backpacking in the St Francois area. They're pretty awful animals and can be aggressive if you stumble across a lot of them.