09/03/2026
Colorado is famously rectangular—at least it looks that way on most maps. Its four borders cut across the landscape instead of following it, including the state line between Colorado and New Mexico, which on your navigation app of choice probably looks perfectly straight. It slices smoothly over the Sangre de Cristo Mountains, cuts through the Old Raton Pass, and bisects the San Luis Valley with an invisible boundary, separating Taos from Conejos in law if not always in spirit. But zoom in and you’ll see that the supposedly straight line is actually strangely jagged. And that wasn’t by design.
In 1925, New Mexico sued Colorado over this boundary. The letter of the law, including both states’ constitutions, defined the boundary between the two as the 37th parallel—but when federal surveyors set out to trace that line over the landscape, they messed up. Not just once, but multiple times over 50 years. The result was a meandering, saw-toothed border. Similar errors all over the state lines left Colorado with a total of 697 sides, making it—according to mathematicians—a hexahectaenneacontakaiheptagon.
In the case of New Mexico v. Colorado, the Supreme Court ruled that the surveyor’s line was, for all intents and purposes, the southern border of Colorado, and it would simply be too much hassle to change the roughly mile-wide strip of mostly unused land. So they tossed out the suit and politely requested New Mexico not bring it up again, for everybody’s sanity. And Colorado, legally, hasn’t been a rectangle since.
—Devin Flores, Assistant Editor and Managing Editor of the Colorado Encyclopedia
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Postcard of Old Raton Pass, once a major hurdle on the famous Santa Fe Trail. History Colorado 2019.13.6334
Early map of Colorado Territory by Samuel Augustus Mitchell, 1862. Courtesy of the Clements Library, University of Michigan
US surveyors in Colorado in the 1870s, mapping a remote location. History Colorado, 83.400.3036
