Remove the lid from the shoebox and cut off one long side of the shoebox for easy viewing. The box now has one side, a bottom and two ends.
Attach wax paper to the inside of the shoebox with clear tape. Pull the paper tightly so it lays flat on the surface.
Mix brown icing with white icing to create a light brown color. Spread a thin layer of the light brown icing on the bottom of the shoebox.
Combine blue icing with white icing to make a light blue. Spread a thin layer of the sky blue icing on the inside of the back of the box. This forms the sky backdrop for the diorama.
Bake two 9-inch round white cakes. Stack the cakes and cover with light brown icing. Sculpt the cake into a mountain with a sharp knife. Make slightly rounded edges on the cake with the flat of the knife to create a weathered appearance. Add a few dots of icing to the bottom of the diorama and place the cake mountain on top of it to stick the mountain to the base. Place the mountain in the corner of the box.
Mix shaved coconut with green food coloring. If the green is too dark, you can mix in a small amount of yellow food coloring to lighten it. Scoop a teaspoon of the coconut onto the bottom of the diorama. Use small dots of light brown icing to glue these edible tufts of grass sporadically around the base of the mountain and along the end opposite the mountain.
Scrape the salt off two to three pretzel rods. Use the icing to glue them into place along the surface of the plateau near the mountain. These represent fallen logs.
Glue a few fresh broccoli spears in place on the ground of the plateau with the icing. Place them toward the back of the box and the side opposite the mountain.