The Tonto Group is made up of the Tapeats Sandstone, the Bright Angel Shale, and the Muav Limestone.

  !   Click each layer in the diagram to see a photograph of the rocks and a description of the environment where they formed. Move your cursor over the image to highlight the featured rock layer. Examine the descriptions to help you answer the question below the diagram.

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.