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Most Minnesotans probably can pick out their state on an unlabeled map. Its distinctive shape, with the Arrowhead pointing east and the Northwest Angle sitting up top like a tiny hat, is hard to miss.

William Lass might know more about that little hat than anyone else. Lass literally wrote the book on the creation of the Northwest Angle. “Minnesota’s Boundary With Canada: Its Evolution Since 1783,” was published in 1980 by the Minnesota Historical Society Press.

And it still bugs the 90-year-old Lass when he sees references to the Angle being formed as the result of a surveyor’s error, most recently cited in a White House petition to give the Angle to Canada.

“I’ve been fighting this legend since 1960,” Lass said last week. That was the year he joined the faculty at Minnesota State University, Mankato, where he taught history until 2002.

“Heaven knows where it started,” he said. “At an Anoka bar, for all I know. Once these things get going, they’re pernicious. They spread by word of mouth.”

Lass, who still lives in Mankato, became interested in the origin of the Northwest Angle when his college students started to ask questions about it. He began looking at the historical record, poring over dozens of maps and hundreds of pieces of correspondence from the Revolutionary War era and later.

He found no surveyor’s error. What he did find, though, was a map that set in motion the creation of the Angle. This map, which Lass’ book cited as “the most important and the most famous map in American history,” was published in 1755. It was the work of John Mitchell, a respected cartographer living in London.

Formation of the Northwest Angle

This 1755 map was used in 1783 to set the U.S.-Canada border at the end of the Revolutionary War, contributing to the formation of what became the Northwest Angle around Lake of the Woods. Many of Minnesota's largest and most notable lakes and water features were drawn wildly out of scale, allowing for some interesting errors. Click image for larger view.

This is an annotated digital map of Minnesota in the mid-1700s, which contributed to the accidental notch at the top of the state known as the Northwest Angle.

Mitchell created a map of British and French possessions in North America — what would later become the United States and Canada. But at the time, much of the area west of the Great Lakes was unknown to Europeans. The mapmaker hadn’t been there himself; instead, he relied on reports from ship captains, fur trappers, explorers and others who had visited the area.

When the Revolutionary War ended, diplomats from the United States and Britain gathered in Paris to hammer out a peace treaty, which included setting the northern border. Using Mitchell’s 1755 map, they decreed that the border would be on a line drawn from the northwesternmost point of Lake of the Woods.

Problem was, Mitchell’s map had Lake of the Woods in the wrong place — and with the wrong shape. It appears on that map as being smaller and more egg-shaped than it really is. He also failed to accurately place the source of the Mississippi River, which also figured into the border line.

In the 1820s, a joint U.S.-British survey determined the accurate placement and shape of the lake. But since the treaty that created the United States had specified the border as the northwesternmost point of Lake of the Woods, the U.S. insisted that it had to stay there.

“You could not negotiate away any part of the treaty under which you gained your independence,” Lass said. “That’s an important legal point.”

And the British weren’t all that interested in claiming the Angle either, he added.

“The U.S. had a long tradition of land acquisition, and they were just plain avaricious when it came to claiming territory,” he said. “The British were a tradition of naval power and building an empire by controlling the seas.”

“So,” he said, “the British were happy to let the Americans expand the frontier.”

Lass realizes not everyone cares about how the Northwest Angle came to be, but he’s determined to set the record straight at every opportunity. And he cautions against being too hard on the mapmakers whose errors set it all in motion.

“Through hindsight we can determine that they were wrong,” Lass said, “but they were accepted at that time.”