Just how durable are beaver dams? A map from 1868 showing beaver dams across a portion of Michigan still exist 150 years later.

The map is from an 1868 publication The American Beaver and His Works, studying beaver habitat around the Ishpeming area in Michigan's Upper Peninsula and shared by AtlasObscura.

When modern day ecologist

Carol Johnston first saw Morgan’s map, she realized she had a unique opportunity to see how the Ishpeming area’s beavers fared as the railroad opened up their territory to human development. Johnston compared Morgan’s map to one she made herself last year using recent aerial photographs, and found evidence that some 75 percent of the dams and ponds that Morgan documented were still discernible. More than a dozen dams and ponds were still intact nearly 150 years later (if you’re keeping score at home, that makes them a little older than some feats of human engineering like the Eiffel Tower), and at least one pond was larger on Johnston’s map than Morgan’s, suggesting it had been built up and raised in the years in between.

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