ok, my dad's gonna bug the heck outta me until i find this out. he wants to know how Disney World makes their rocks, such as for Big Thunder Mountain and such.
The imagineers first make a foam model. The model is scanned into a computer using lasers for precision. Then they use the computer data in a custom designed machine that bends the rebar to the shape as given by the computer. Wire mesh is put over the rebar, then it is covered with a substance called 'mud', which is similar to cement. Finally, they paint the rock to match the themed area.