The world's largest interpretative geosciences exhibit is being constructed along the South Rim of the Grand Canyon between Yavapai Observation Station, which houses a recently remodeled geology museum, and Grand Canyon Village. The 1,800 meter-long Trail of Time [right, photo credit ASU] will represent the 1.8 billion year history of the rocks exposed in the Grand Canyon marked with inset bronze disks, each meter symbolizing 1 million years of Earth's history.
For nearly 10 years, ASU geoscience professor Steve Semken has worked with founding Trail of Time team members Karl Karlstrom and Laura Crossey, both of the University of New Mexico, and Michael Williams of University of Massachusetts (one of my alma maters!). This group envisioned turning a Grand Canyon hiking trail into a walking timeline that would represent the magnitude of geologic time. The Trail is expected to be completed in 2010.
Steve says eventually they would like to extend the trail all the way out to Maricopa point which will be 4.5 km, taking people to the very beginning of the earth, 4.5 billion years.