These three layers are considered to be a group, because
the environment in which they formed changed very little
from deposition of one layer to the next. A continual
gradual change in the environment resulted in deposition
of all three layers. Examine the descriptions for the
three layers and consider what would account for the
sequence of sandstone, shale, and limestone observed.
7. Describe the changing environmental
conditions that resulted in the formation of the three
layers of the Tonto Group.