The Monsoon — a stop on the Coronado Trail Scenic Byway.
If you're driving this between about early July and mid-September, you're in monsoon season, and you need to know how it behaves because it will affect your day.
The pattern is remarkably reliable. Mornings are clear and beautiful. By late morning cloud starts building over the high country. By early afternoon those clouds are enormous, dark-bottomed and towering, and then somewhere between one and five in the afternoon they let go — hard rain, spectacular lightning, occasionally hail, usually for less than an hour. Then it clears and the evening is washed and golden and smells wonderful.
For a driver on this road, three things matter. Lightning: you are on an exposed ridge at nine thousand feet, so don't be standing at an overlook when it starts. Water: the road has no shoulder in places and sheets of runoff cross it. And flash floods lower down, in the desert section, where a dry wash can become a wall of water from rain you cannot even see falling twenty miles away. Never drive into a flooded wash. Arizona genuinely has a law about people who do.
The upside is that monsoon afternoons produce the most dramatic skies in North America. Just be somewhere sensible when it arrives.