dressed up the mountainsides. The rocky gorge and the rushing river at its bottom were matched by using photographs of the actual scene as guides.
There's more to creating a realistic river in flood stage than you might think, even in miniature. One of the problems is the sheer volume of water required. This was solved by storing all the water in a small reservoir and in a number of huge dump tanks, all upstream out of camera range. When the water was released into the river a satisfactory flood came pouring downstream.

But the torrent didn't have the swirling white crests and the swift treacherous currents of an actual river in flood, so these were added artificially. Water pipes were laid in the river bed with spray heads attached to provide swirls of current.
Lee Zavitz explains that building the miniature trestle was easy, but engineering it so that it would collapse at the right time and in the right manner took a lot of thought. The trestle was built of wood, each small stick representing an actual timber in the real structure. Construction details had to be perfect. A flaw such as a hammer ,mark around a nail would be magnified to the size of a basketball on the screen, giving away the whole scene.

"After the trestle was built we placed a four-inch pipe across its bottom, extending from one-side of the river to the other," Zavitz says. "The pipe was hidden by the water. Then we ran concealed cables from various parts of the trestle down to the pipe and attached them at different points. Thus, when the pipe was rotated by a motor the cables wound around it. The cables tightened one at a time and successively brought down different portions of the trestle. The whole collapse had to occur in just the same way that an actual trestle would weaken and fall."
The scaled-down train used in the scene was a modern miniature that was rebuilt to match the actual train used in Colorado. Such details as the engine cab, stack, headlight and whistle were all reproduced exactly. Batteries were used for interior lighting. The engine had its own boiler and produced its own steam. Black smoke for the stack came from a smoke cartridge.
"It would have been simple to send the train across the trestle under its own power," Zavitz remarks, "and we might have done this if the story called for the train to run off the trestle and crash in the river. But the running of the train