Titus Canyon, in Death Valley National Park, CA, is a popular dirt road that crosses through the heart of the Grapevine Mountains and descends through a narrow, deep canyon. Along the way, it passes through 550 million years of history including dramatic stacks of limestone and near-shore sedimentary deposits, much younger rocks containing fossil mammals and colorful volcanic deposits, and a 1920s ghost town founded on a famous con (read up on the history of "Leadfield" for that one).
Flash floods in the summer of 2023 washed out the road below Leadfield, lowering the canyon bottom to bedrock in a number of places and erasing most traces of a road having ever existed there. It won't reopen to vehicle traffic for a while, but the whole canyon is open to hiking. It's a much different experience to walk through the twisting narrows compared to driving the same route.