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