Sanderson was leading them, though close behind came several of the Double A men, their faces set and grim; and then one of Williams' men, a young fellow who had admired Mary Bransford from afar; then some more of the Double A men, and Williams and the remainder of his band of engineers. There was no word spoken. In a few swift sentences Sanderson had told them what had occurred, and there was no need for words as they fled southwestward. For a few miles the trail was hard and smooth, and the posse made good time. Then they struck a stretch of broken country, where volcanic action had split the surface of the earth into fissures and chasms, thus making speed impossible. It took them long to cross the section, and when it was behind them they found themselves in a hilly country where the going was not much better than it had been in the volcanic area. The trail was narrow, and they were forced to travel in single file. Sanderson led the way, Streak thundering along, a living blot splitting the brown, barren wasteland, followed closely by other blots, rushing over the hazardous trail, the echoes of their passing creating a rumble as of drumfire reverberating in a canon. They came to a point where the trail led upward sharply, veering around the shoulder of a hill and dropping precipitously into a valley. For an instant, as the riders flashed around the shoulder of the hill, they caught a glimpse of a group of riders coming toward them, visible to Sanderson and the others as they were for a second exposed to view in a narrow defile. Then the view of them was cut off, and Sanderson and the men following him were in the valley, riding desperately, as before. Still there had been no word said. Sanderson had seen the oncoming riders, but he attached no importance to their appearance, for cowpunchers often rode in groups to some outlying camp, and these men might belong to some ranch in the vicinity. There was a straight stretch of hard, smooth trail in the center of the valley, and Sanderson made Streak take it with a rush. Sanderson grinned grimly as he heard the other men coming close behind him--they were as eager as he, and as vengeful. Up out of the valley went Streak, running with long, smooth leaps that gave no indication of exhaustion; Sanderson patted his neck as he raced upward out of the valley and into the defile where they had seen the riders. Sanderson was halfway up the defile when he was assailed with the thought that by this time--even before this--they should have met the other riders--had the latter kept the trail. Struck by a sudden suspicion that there was something strange about the disappearance of the riders, Sanderson abruptly pulled Streak up. The other men were some distance behind, and Sanderson slipped out of the saddle to give Streak a breathing spell.