La Bajada Hill served as Route 66 during the 1920s and the early ’30s, although the path itself dates to the 1500s as part of the Camino Real. The steep and narrow roadway featured 23 switchback curves. So the locals felt obligated to warn motorists what they were getting into.
Incidentally, the road is little-changed in the 90 or so years since Route 66 was realigned. It’s eroded in spots, and only four-wheel vehicles should attempt to drive it. So the re-created sign’s warnings are still relevant. If you’re wanting to explore La Bajada Hill, it’s best done while hiking.
Brian Shawn McClenahan of The Sign Guy in O’Fallon, Missouri, was commissioned to paint the sign. He created a time-lapse video of how he made it which, helpfully, includes a rare image of the bullet-ridden original sign: