Geological Survey Professional Paper 669 The Colorado River Region and John Wesley Powell

During the past 100 years, increasing investigation of stratified rocks in the Grand Canyon has been responsible for a rapid expansion in the accumulation of facts; as might be expected, these new facts have been significant in the evolution of ideas about the regional history. From the number of recent discoveries that have modified earlier concepts, it is evident that changes in our ideas concerning Grand Canyon rocks may be expected to continue for a long time. This is especially true in such features as the genesis of certain rocks, the significance of many fossils, and various environments of deposition.

As Powell recognized during his boat trips in 1869 and 1871-72, clear exposures of the strata and the general lack of structural disturbance offer nearly ideal conditions for the study of these rocks. Many geologists subsequently have realized that opportunities are exceptionally good for testing theories concerning natural processes and for demonstrating the detailed record of such phenomena as transgression and regression, cyclic sedimentation, facies relationships, diastems, and others. Thus, the Grand Canyon has proved to be one of the world's finest laboratories for illustrating various geological principles, especially those related to the history of stratified rocks.