In the San Diego work, a huge mass of rocky hillside overhung the cañon
which was to be dammed, and at the bottom of which the river flowed.

A cañon is, as you doubtless know, a deep gorge or ravine, formed by the
river that flows through it, and which little by little has worn away its
bed until it has cut deep down into the heart of the land, hundreds of
feet below its original level.

As we have said, the plan for the San Diego work was to build a dam across
the cañon, and keep the waters from flowing away.

The engineers thought that if they could only take this huge mass of rocky
hill and drop it into the cañon, it would make their work very much
easier, as the task of getting enough stone down to the bottom of the
gorge to build their dam was by no means an easy one.

They thought the matter out, and finally decided to try and move the
mountain-side into the cañon.

They laid their plans, and for two months were busy preparing for the
great move.

They tunnelled the hillside in all directions over the section which they
desired to move, and in these tunnels laid mines of giant powder or
dynamite.

These mines they connected with electric wires, and when all was ready,
the various wires were gathered into one bunch, and taken across the gorge
that was to be filled up.