The summit of the bare walls rose higher and higher. Far above the cut a vulture wheeled. The sun beat down into the canon, for it was now mid-forenoon, and, the breeze having died, the party of riders began to suffer from the heat.
"I'm melting," declared Bess. "But that's a small matter. I was getting too fat, anyway."
"Listen!" commanded Rhoda suddenly.
They heard then a growing sound like the rolling of many barrels at a distance. It was not thunder. The sky was as clear as a bell.
"Quick!" exclaimed Rhoda. "We must get up yonder in that cleft!
See? And keep a tight rein on your ponies."
They rode quickly off the trail, while the strange sound grew in volume. It certainly was something coming down the canyon; but the huge boulders shut out all view of what lay thirty yards away from the party.
They reached a small cleared space against the foot of one cliff, but some yards above the bottom of the canyon. Now, as the growing sound came nearer, Nan shouted:
"I know what it is! It's the herd of horses."
Rhoda nodded. The clatter of the countless hoofs came nearer and nearer. The girls and Walter dismounted, and Rhoda warned them to stand in front of their mounts and keep the bridle-reins in their hands.
They could not yet see the head of the herd; but above the boulders they saw a cloud of dust rising. This dust rolled down the canyon and reached the observers first. Then appeared several horsemen riding at a sharp canter. The range horse almost never trots.