The Grand Staircase
The image above shows how the geologic formations of the Grand Canyon form part of a larger complex that includes Zion and Bryce Canyons to the north. 

Although the Grand Canyon formations are, for the most part, millions of years older (shown in the image below) than those in either Zion or Bryce Canyons, they are now exposed because they were eroded by the Colorado River and its tributaries as the Kaibab Plateau began to uplift.

The Grand Staircase

The image above shows the formations in the Grand Canyon, those in Bryce and Zion Canyons to the North and their relative ages.  As illustrated in the first image, the formations that are exposed in the Grand Canyon actually underlie those in the other canyon formations.  This region contains a fairly complete record of life on earth as it evolved over hundreds of millions of years.  It is interesting to see how the environment in a relatively small area can change back and forth from marine (with fossils of aquatic organisms) to terrestrial (with fossils of land plants, and animals - which can include footprints and burrows).  The processes that formed these layers and formations are interesting and complex, but good information can be found online.  I simplified the image to show only the regions documented above, however these and related formations encompass a larger area that include Colorado and New Mexico as shown here.

Some References:
Geology of Grand Canyon Rock Layers - a summary of all the formations exposed in the Grand Canyon.
Layers in Time - another description of Grand Canyon geology and fossils.
Geology of the Grand Canyon - this is a fairly complete overview of how the Grand Canyon might have formed.
Fossils of the Grand Canyon - an introduction to some of the fossils that can be found within the Grand Canyon.
Geologic Map of the Grand Canyon and Vicinity - a vertical map of the region with the formations labeled - a different perspective than the cross-sectional views normally seen.
Geological History of Grand Canyon - a somewhat wandering description of the formations and fossils - keep a diagram of the layers handy to follow the discussion.