.

SET AFOOT.
The tracks of the six horses led down into a rock-bottomed arroyo so deep in most places that all view of the surrounding mesa was shut off completely, save where the ragged tops of a distant line of hills pushed up into the dazzling blue of the sky.

The heat, down here among the rocks, was all but unbearable; and when they discovered that no tracks led out of the arroyo on the farther side, the Happy Family dismounted and walked to save their horses while they divided into two parties and hunted up and down the arroyo for the best trail.
It was just such vexatious delays as this which had kept them always a day's ride or more behind their quarry, and Luck's hand trembled with nervous irritability when he turned back and banded Applehead one of those small, shrill police whistles whose sound carries so far, and which are much used by motion-picture producers for the long-distance direction of scenes.
"I happened to have a couple in my pocket," he explained hurriedly.

"You know the signals, don't you?
One long, two short will mean you've picked up the trail.

Three or more short, quick ones is an emergency call, for all hands to come running." "Well, they's one thing you want to keep in mind, Luck," Applehead urged from his superior trail craft.