Building the model
Physically, the model resides in a plastic storage box big enough to hold a 12.5 X 18 inch polystyrene platform. The box needs a horizontal line (made with permanent felt tip pen) marking on the outside prominently labeled "Sea Level." Depending on how the rim of the storage box is designed, this should be no more than a couple of inches below the top of the box.
The platform, painted black to represent Precambrian rocks exposed at the bottom of the canyon, can be raised or lowered. The raising and lowering mechanism can be constructed from two strings, two half-inch by-half-inch by eight inch strips of wood, and two rubber bands.
For the layer sets, two stacks of ten 12.5 X 18 inch foam pieces are cut from carpet underlayment. Underlayment (the kind manufactured by binding multiple small pieces together) has a chunky texture that is more rock-like than ordinary foam rubber. The first stack needs no further work than to paint it according to the colors of the rock layers.
The other stack is cut into three sets of cutaways that allow the progressive "erosion" of the canyon. When all three cutaway sets are removed, the model represents the eastern part of the canyon (the part tourists see) as it appears today. This pattern was developed by tracing from the generalized geology displayed on the state geologic map of Arizona.
The cutout patterns are available here as apdf file (452 K). To print this file out, set your printer to legal size. You will need 30 sheets of legal-sized paper.
Once the three sheets for a layer are pieced together and clipped to the foam layer, the layer is cut along the pattern lines. In some places the cutout lines are replaced by bands of gray to represent sloping canyon walls – here the scissors should be tilted with a slope toward the bottom of the canyon. When the pieces are cut, the parts of them that will be exposed to view are painted according to the layer color scheme.
When all the layers have been cut, a glue gun is used to assemble the pieces into the three cutaways plus the final canyon model.