Everything changes over time. Rivers change course, widening, narrowing, winding where once they were straight. Landscapes change. Even the magnetic North Pole changes. So, too, has Bob Bergantino’s study of Lewis and Clark’s legendary journey across North America changed — from an interest in history to a hobby that nearly has become a life’s work.

Known in some circles as the “mapping guru,” Bergantino has spent his spare time during the last 30 years investigating and pinpointing the route and stops that Meriwether Lewis and William Clark made — especially in Montana — during their expedition from St. Louis to the Pacific Ocean. Of course, Bergantino points out, pinpointing does not necessarily mean finding the exact location of a campsite.

“We have to redefine what we mean by exact,” says the 59-year-old associate research professor of hydrogeology at UM’s Montana Tech in Butte. “A point on a map may cover 100 square feet, or 1,000. How close can you come?”

Not close enough, in many cases. According to Bergantino, many historical markers and maps proclaiming “Lewis and Clark camped here” are off as much as several miles. At Travelers’ Rest, which the expedition so named because its members paused to rest there before crossing the Bitterroot Mountains south of Missoula, a historic marker tells today’s travelers that Lewis and Clark camped at the mouth of Lolo Creek. Bergantino says the real camp is at least 1.5 miles upstream. Another sign at the mouth of Missoula’s Rattlesnake Creek claims that Clark camped there on July 3, 1806, but according to Bergantino’s calculations, the camp actually was three or four miles to the west, near Missoula’s airport.

Near Helena yet another sign, which is being modified by the Daughters of the American Revolution, says the expedition’s campsite was three miles downstream from the actual campsite at Gates of the Mountains.

Bergantino, who has taught and conducted research at Montana Tech for more than 25 years, is known nationwide as an expert cartographer of the Lewis and Clark expedition, consulting with everyone from local amateur historians and historical organizations to the National Park Service, U.S. Forest Service and editors such as Gary Moulton, a professor of history at the University of Nebraska-Lincoln who has edited a 13-volume edition of Lewis’ and Clark’s diaries. Bergantino has created many maps, including one of the expedition’s route through Montana that he donated to the Portage Route Chapter of the Lewis and Clark Heritage Foundation in Great Falls.

“(Bergantino) is very well known for his work,” says Jane Weber, director of the National Historic Trail Interpretive Center in Great Falls. “He’s really an expert in deciphering the field notes in the journals and Clark’s maps and determining the relationship to current landscapes.”

Although modest and unassuming about his expertise, Bergantino is “very generous with his time,” Weber says. When the center opened in 1998, Bergantino not only helped with the exhibit on Clark’s cartography, he also helped draft the text that tells visitors about the displays. “He’s a terrific resource for the state of Montana,” Weber says. “And he certainly has been a valuable asset for the community of Great Falls.”

As a research professor in Montana Tech’s Bureau of Mines, Bergantino no longer teaches classes. A major portion of his work is helping people around the state, and sometimes state or local agencies, who have questions about water — how to locate it, what’s in it, how deep one has to go to find it. He also helps Tech students who are working on related projects, such as determining the water resources for a town. And, just as he does in his work with Lewis and Clark, he spends most of his time working with maps.

“My specialty is really cartography,” Bergantino says. “Fully 70 percent of my time is spent working with maps — geologic maps, hydrogeologic maps.”

Bergantino’s love for Lewis and Clark’s adventures arose naturally out of a lifelong interest in history. Born in Glasgow, Bergantino lived in many Montana towns, his father being a surveyor for the U.S. Army Corps of Engineers.

“My dad was a self-taught historian,” Bergantino says. “He was fascinated by history. Part of his interest was passed on to me.”

After graduating from UM in 1967 with a geology degree, Bergantino longed to go to sea. He joined the U.S. Navy Oceanographic Research Program and, stationed in Washington, D.C., started applying his mapping ability.

On many trips home, while driving across open spaces in eastern Montana, Bergantino developed an interest in Lewis and Clark’s trip across the state. He looked at books on the subject in Washington but found that descriptions of the expedition’s campsites were vague.

“I thought I could do better than that,” he says.

He read Lewis and Clark’s journals and Clark’s descriptions of the land and waters. Then he dug up U.S. geological maps and started plotting sites.

Lewis and Clark surveyed their entire route — Clark was actually the expedition’s cartographer — using a magnetic compass, a sextant and a survey instrument called an octant, Bergantino says. They recorded their latitude, longitude, distances and what they were seeing around them. Using this journal, Bergantino started plotting the explorers’ daily route.

But plotting sites from Clark’s writings and maps of that day onto today’s topographical maps was a challenge. Rivers change, sometimes dramatically over 200 years. There’s even a change in magnetic declination, which President Thomas Jefferson had asked Lewis and Clark to study on their journey to determine the location of the magnetic pole.

Bergantino also began to see how rivers had changed over the years. In some places, Lewis and Clark’s route, which followed the rivers, was now as much as seven miles away from the water.

Lewis and Clark took their bearings by magnetic compass, Bergantino says. And their direction was estimated. They described what was around them at that point — a bluff, a cliff, the junction of a creek. Bergantino looks at all the clues in trying to pinpoint a location.

“I look at the campsite and see how it fits the criteria given in the journals,” Bergantino says. “If there is very specific information, I try to make sure it all fits.”

The professor says he can be pretty accurate about the location of some campsites, but no one can be absolutely certain about an exact campsite, he says.

Looking at all the clues, Bergantino says, he usually can get to within 500 feet of a campsite.

“I try to find the sites as close as I can. But it doesn’t matter if I’m off 200 feet as long as I understand what they saw, what they felt. I can be part of that expedition in spirit.

“Reading the journals, you see history developing. The adventure unfolds every day. It’s been a real time-travel trip.”

Bergantino has traveled Lewis and Clark’s trail himself, all the way across the country, by car or sometimes by plane. He has presented his findings and his maps in meetings, in professional papers, in lectures and on field trips with groups of people from all walks of life.

He has consulted with Moulton on the journals for about 20 years, he says. He also has worked with Joe Mussulman, a former UM music professor who leads a team designing the University’s “Discovering Lewis and Clark” Web site. And, using a prototype he built himself, he will show Mussulman how the octant that Clark used works.

Bergantino also has spent some time checking Lewis and Clark’s math — their calculations for determining their latitude and longitude. He succeeded in recalculating the latitudinal observations, but the longitudinal calculations are complex.

“Mostly, they were about 10 to 15 miles off in latitude, which is not bad” considering their instruments, Bergantino says.

As far as Bergantino knows — and Jane Weber and Ella May Howard as well — no one has researched the geography of Lewis and Clark’s route to the extent that Bergantino has. “A few people have worked on a few sites, but none on this scale,” he says.

Through all the years he has studied Lewis and Clark’s journey, Bergantino has never been completely satisfied that he has found the exact route. He had determined one campsite near Twin Bridges but later changed his mind and placed it a half mile away from his first site.

“It might be that I’ll never succeed in feeling completely comfortable,” he says. “There’s a lot of places I’d like to go back and re-evaluate.” He has no plans to stop his lifelong study.

“I learn as I go along — about Lewis and Clark, about the rivers and how they change. I hope I never come to the end of it.”