What's Curious about
the Loess Hills?

topographic map showing bluff & ravine Let's begin with a glance at the topographic map at the right, showing an area of the Loess Hills just south of Natchez, Mississippi. To orient yourself, the left part of the map with relatively few lines is fairly level swampland, while the right part with many lines is the nearby hilly upland. A steep bluff forms the transition between swampland and upland. The brown lines signify changes of 20 feet in elevation, so the heavier brown lines represent 100 feet of elevation change between them. With this in mind you can see that in some places the bluff rises over 100 feet in a rather steep slope, and that sometimes the elevation change from the swamp to the nearest hill top is over 200 feet.

Notice that the large bayou, with very steep sides about 100 feet high, has numerous "arms" branching off more or less at 90 degree angles. Also notice that the streams in the bottom of the bayou are fairly short, and gain elevation rather quickly -- they are fairly steep, especially where the ravines narrow.

An important point about the ravines not apparent on the map is that many, perhaps most, bayous, or ravines, instead of draining directly into the lowland below the bluff (to the west, toward the Mississippi River, thus cutting through the bluff face), drain in the opposite direction. Water flowing in them drains into streams and rivers behind the bluff (on the eastern side), and then these streams and rivers typically, eventually, cut through the bluff someplace and flow into the Mississippi.

By the way, if you'd like to find this particular spot on your own map, the mouth of the large bayou lies at approximately N 31° 28' 30", W 91° 25' 45".

Dr. Sigrid Liede standing in a u-shaped sunken road, one of the "old Trace" sections of the Natchez Trace; this is in MississippiAt the left you see something else strange about loess. That is, when it erodes -- and it turns to gravy when it's wet -- it forms steep-walled gullies. The picture shows an old section of the historic Natchez Trace. Where the Trace passed among hills not capped with loess, "sunken roads" developed in U-shaped gullies did not form. If gullies formed, the gully walls were much less steep.

So, all this is curious. If you were to throw a dart at a map of the whole earth, the chances are slim that your dart would land at a point within a hundred miles of such a feature as is shown on the topographic map. This kind of very long bluff rising above swampy lowland, abundantly intersected with deep, steep-walled bayous, or ravines, and sunken roads in U-shaped valleys is simply special. It's curious. If you live near this bluff, you have reason to feel that you live near something out of the ordinary. Our Loess Hills are worth talking about.

Now, the question arises: How did this very hilly area with its bluff get the way it is? Anyone who knows that rivers and streams erode flat floodplains for themselves can guess that the Mississippi has simply wandered around within its floodplain for millions of years, and in the process has eaten away at the uplands around it, leaving this long bluff at the limit of its easternmost meanderings. As it turns out, this guess explains part of the bluff's reason of being, but not all. Anyone standing in the gazebo in Natchez's Bluff Park overlooking the Mississippi River can sense that there's more to the story than that.

For one thing, even on the clearest fall day when it seems you can see forever from that gazebo, one thing you cannot see across the river in Louisiana is an upland on the other side. For twenty-five miles west of Natchez, curiously, there's no elevation in Louisiana rising higher than a few feet above the surrounding landscape. Isn't that a bit large to serve as a simple floodplain, even for such a magnificent river as the Mississippi? Fact is, this twenty-five-mile gap is actually about the narrowest point in the lower Mississippi River's floodplain, if floodplain is what it really is. Moreover, when uplands do emerge in Louisiana, as at the Sicily Island Hills, they do not form a great north-and-south-running bluff like ours. If the Mississippi had carved the bluff we're perched on in Natchez's Bluff Park, wouldn't there be a twin bluff on the river's western side?

There's something else curious about this bluff at Natchez. At the tops of most cliffs and bluffs, don't you almost always find outcropping rocks? Well, there are no outcropping rocks at the bluff at Natchez, and if you find outcropping rocks elsewhere along the bluff from Louisiana to Kentucky, they'll be rare, and of a relatively soft, half-formed nature, often so soft that they can be scratched with a thumbnail. Why doesn't our bluff have outcroppings of hard rocks?

The mystery of this area becomes full-blown if you speak with Natchezeans who know a little about their area's prehistory, for they'll tell you why Mammoth Bayou in north Natchez is called what it is. It's because in that big ravine people have found bones of animals they called mammoths -- enormous, elephantlike animals living in this area during the Ice Age.

upper molar of the mastodon, Mammut americanum Actually, Mammoth Bayou's "mammoths" were really mastodons. Mammoths are very rare in loess because mammoths live in grasslands, and, at least in the Natchez area, forests were present as the loess was being deposited. Mastodons browsed on leaves and twigs in forested areas, so they were right at home as the loess settled around them. At the right you see a very worn upper molar of the mastodon Mammut americanum, found in a local bayou, or ravine, by amateur fossil-hunter Betty McKay of Natchez.

Tooth of Ice Age horse Equus complicatus, photo by Karen Wise of Kingtson, MississippiIn fact, not only have mastodon remains been found around Natchez, but also remains of ancient ground sloths, a form of native horse that was a big, hulking, draft-horse-like creature, and many other extinct, Ice-Age animals. At the right is another of Betty McKay's local finds, the upper cheek tooth of the large (the size of a big draft horse today, like a Budweiser Clydesdale) Ice Age horse Equus complicatus. Thanks to Earl Manning of Tulane for the identification of both of these specimens.

Also curious is that the remains of these large animals have always been buried deep inside or below the loess, not atop it... Yes, something curious -- quite possibly even something majestic in scope -- has been going on here. This long bluff at Natchez and all along the western boundary of the Loess Hills has a story to tell...