It's fairly easy to think up logical explanations for stuff that happened a thousand years ago. Go ahead, try it yourself.

Whenever we travel, my wife and I manage to find out-of-the-way sites that even most locals haven't heard about. We once tried to get directions to some dinosaur footprints in New Mexico. The best the hotel clerk (a native of the area) could tell us was to stay away from the nearby lake, because a second cousin had drowned there. More than 30 years ago.

During a recent trip to Florida, we tried to see two things in particular: manatees and big mounds of seashells deposited by prehistoric Indians that have a name I can't remember. The mounds, that is. Well, I can't remember the name of the Indians either, for that matter.

We found the manatees, also known as sea cows, in an old canal that is now part of the national seashore. There are only 2,700 manatees left in the world, or so we were told, and we managed to watch 9/2,700ths of the world's population cavort and munch underwater grass. What does that work out to? About 1/300th of the world's manatees? We obviously don't go searching for math museums.

I am frequently amused when we find prehistoric stuff. Well-paid and highly educated prehistorians have drawn conclusions based mostly on speculation. For example, we saw some effigy mounds on a bluff overlooking the Mississippi River in the northeast corner of Iowa a few years back, and there was a uniformed ranger to tell us he didn't know why the Indians made huge mounds shaped like a snake. Then he spent 30 minutes telling us what he thought -- all based on guessing.

Those seashell mounds, we were told, had ceremonial significance. True, the mound we saw was an enormous pile of shells -- enough that it looked like a small hill. Of course, in Florida any pile of anything looks like the Rockies. But that doesn't remove the shadow of doubt I have about those old seashells.

First of all, I don't know for sure those shells have been there for several centuries. Maybe some 1920s land speculator piled them up to make ready for beach homes. Or maybe the shells are hundreds of years old, in which case we know that seashells never rot, so I wouldn't recommend putting them in compost piles -- a lesson those prehistoric Indians might not have learned.

Last weekend we saw something closer to home attributed to prehistoric Indians. It was a stone fort in the Shawnee National Forest, which covers most of Southern Illinois. The experts speculate the stone walls built across high bluffs were put there for protection or to corral animals some 1,000 to 1,200 years ago.

How do they know? If memory serves, prehistoric means they didn't leave any notes explaining why anyone, modern or ancient, would pile up rocks in a fairly straight line from one side of a bluff to the other.

I happened to notice that the roadways in the state park where we saw the stone fort also had been decorated with stone retaining walls that looked very much like what the Indians purportedly built before the Battle of Hastings. I also noticed that a long stretch of creek bed had been similarly walled. The park officials told us the decorative walls were put up as a WPA project during the Depression.

Sure, but what will archaeologists think a thousand years from now? That 20th-century Southern Illinoisans herded white-tail deer along asphalt paths lined with stone walls? Has anybody thought about chiseling a message into one of those rocks to avoid confusion in the year 2996?

To pass the time (vacations give you extra time to play with), I like to think up my own explanations. Some of them sound just as plausible as the high-paid guesses. For example, I think those seashell mounds are the remains of early-American road builders who thought ground-up shells would make good paving material but, unfortunately, hadn't invented a grinder yet.

Or what about this? I think those stone walls in the Shawnee National Forest are the remains of an ancient savings-and-loan chain, left over from the days when a man's rock pile was his life's wealth. I noticed something the archaeologists apparently have overlooked. The bigger rocks are at the bottom, with the smaller ones on top. That could lead a thoughtful and careful observer to the conclusion that the twenties are on the bottom and the fives are on top. Or something like that.

And those footprints in New Mexico? Maybe a dinosaur made them. Maybe a prehistoric jokester was just having a little fun on vacation. Who knows?

~R. Joe Sullivan is the editor of the Southeast Missourian.