One of the most amazing learning experiences I have ever enjoyed is 'The Trail of Time', an interpretive walking timeline trail, "that focuses on Grand Canyon vistas and rocks to guide visitors to ponder, explore, and understand the magnitude of geologic time and the stories encoded by Grand Canyon rock layers and landscapes."
The 1800 metre path represents the 1.8 billion year history of the rocks exposed in the Grand Canyon. It is marked with inset bronze disks, each meter symbolizing 1 million years of Earth's history. Along the route one can stop to see a representative rock of the age. As well, you can look out at the rocks which are embodied in the canyon.
For several days intermittent rain has dumped more than 4 inches and fog has shrouded the canyon occasionally. Patience is needed to wait for the vistas to return; meanwhile, the trail of time was most serendipitous.