Its only practical outlet was that guarded by the sheepmen.

But a short way up the canyon there was a spring in the hills, which found its outlet in a narrow stream that ended in a small waterfall at the edge of a cliff.

Mart figured on his force entering the canyon, stampeding the sheep, and driving them over this waterfall.

It was as simple as it was cruel, but you may have noticed that it takes clever people to think of simple things, and Mart Cooley was proving almost as clever with his mind as he was with his guns.

For Mart also figured on the effect on the sheepmen's nerve when they found their herds gone, and their water from the tank giving out.
Under cover of darkness Mart led about fifteen men around the hill, which they skirted, and, giving the ranch house a wide berth, made their way toward the mouth of the canyon.