Take the cover off a shoe box. Stand the shoe box on its side. Color the inside of the shoe box. Make the bottom side of the shoe box the ground by drawing grass, roads or anything that might appear around the base of the mountain. Use tin foil to create a lake or stream. Color the backdrop of the shoe box (the part that is normally the bottom). Draw distant mountains and sky. Add birds if desired. Continue coloring sky on the top side of the shoe box. Stretch out some cotton balls and glue them onto the background as clouds. Cut a hole in the top side of the shoe box to let in more light if needed.
Mold clay into a shape of a mountain. Build it to the right height so that it fits inside the box. Use brown, gray or another color that resembles a natural mountain. Make your mountain bumpy and irregular to look more realistic. Spread glue on the base of your mountain and place it inside the shoe box standing upright. Smear the edges of the mountain's base down on the shoe box.
Collect grass, small twigs, pebbles/sand to add to the bottom of the shoe box around the base of the mountain. Spread a thin layer of glue wherever you want to attach natural materials. Stick some twigs or pieces of an evergreen tree into your clay mountain to create the effect of trees.