It's hard to look at Vermont's rolling hills and fertile river valleys and think, ''Woolly mammoths roamed here,'' but it's true. There was even a woolly mammoth that met its end somewhere on the hill in my backyard.

No, I'm not hallucinating.

A five-foot long tusk, found by Col. Rolla Gleason in 1865 in Richmond, is on exhibit at the University of Vermont's Perkins Museum of Geology. To understand how the tusk found its way to the hills of Richmond, you have to understand a little bit about Vermont's recent geologic past. And you have to do a little sleuthing, like Walter Poleman of Richmond did to figure out the tusk's complete story.

First, the history: At the height of what geologists call the Wisconsin glaciation, which stretched from about 2 million years ago to about 12,000 years ago, two ice sheets covered two-thirds of North America. The Laurentide ice sheet extended from the Rocky Mountains to Greenland, and the Cordilleran ice sheet stretched from northern Alaska to parts of the Sierra Nevada. At its greatest extent, the Laurentide sheet stretched as far south as Long Island and coated Vermont with a mile-thick sheet of ice. Vermont of 13,000 years ago was just emerging from this mantle of melting ice.

As soon as the ice melted away, woolly mammoths and other large animals, including caribou and a giant beaver six feet tall, roamed the countryside, feeding on the tundra lichens and little willows that surely grew in the shadow of the ice. Not far behind came Vermont's first residents, Paleolithic natives who hunted mammoths and other creatures for food.

Now comes the sleuthing part.

Poleman, an administrator and lecturer with UVM's Field Naturalist Program, wanted to know exactly where in Richmond the tusk had come from. Unfortunately, there's precious little information about the tusk at the museum, other than the town where it was found, and the finder. So Poleman started some detective work.

One of Poleman's geographer friends, Jane Dorney, found a reference to the find in an 1866 magazine, ''Hours at Home: A popular magazine of religious and useful literature.''

The magazine gives a general description of where the tusk was found, and how high it was above the Winooski River. That turns out to be a key piece of information because just after the ice sheets melted out of Richmond, the valleys filled up with water -- first when the glacier backed up smaller lakes in the Winooski River drainage and beyond, as far east as Williamstown, and later, about 12,000 years ago, from a lake that covered much of northwestern Vermont and as far south as Fair Haven and Rutland. The lake, called Lake Vermont, was caused when the ice sheet blocked the northward drainage of Lake Champlain. The hills that became islands in these big lakes are still covered with lake and beach deposits -- only the deposits are stranded high on the hillsides, far from any present-day water.

Poleman thinks that the descriptions in the magazine match up with the time when Richmond village was drowned underneath Lake Vermont. The mammoth whose tusk feeds our curiosity today wandered the town's hills, when they were nothing more than foothills, and met its end in a swamp where conditions were right to preserve the tusk.

No one knows if there's more woolly mammoth remains in the swamp, because Gleason stopped digging once he found the tusk, and never found anything else. At least not that we know about. Poleman figures someday he'll round up a mess of graduate students and head off to some likely swamps in the hills around Richmond to see what he can find.

I hope to tag along. One of the things I love best about the Vermont landscape is looking at it and knowing that not so long ago, it was covered with ice and woolly mammoths dodged hungry natives.

Right in my backyard.