“I—–­I guess I need a guardian,” said the lad rather weakly.

“Yes, you probably would have been killed by the smaller pieces that broke off,” answered Nance.  “Be content to stay where you are.”

“How long have we got to stay cooped up in this half cave?” demanded Stacy.

“All night, maybe,” answered Dad.

“Good night!” said the fat boy, Slipping down until he had assumed a sitting posture.  He lay down and was asleep in a short time.  Stacy woke with a start when another giant rock smote the wall just above their cave, exploding into thousands of pieces from the violent contact.

“Stop that noise!   How do you suppose a fellow’s going to sleep
when-----”

Stacy struggled slowly to his feet when he saw the drawn faces of his companions.

“Was that another of them?” he asked hesitatingly.

“Yes,” answered Tad, with a nod.  “It is grand, but terrible.”

“I don’t see anything grand about it.  I guess I won’t lie down again.  I never can sleep any more after being awakened from my first nap,” declared the fat boy.

No one slept for the rest of the night.  The bombardment continued at intervals all through the black, terrifying night.  The Colorado, into which billions of gallons of water had been dumped, was rising rapidly, an angry, threatening flood.

“Is there any danger of the river overflowing on us?” asked Professor Zepplin.

“No.  No single night’s rain would do it.  The rain is pretty nearly ended now, as you can see for yourself.  But there’s no telling how long those fellows will continue to roll down.  I’ve seen the same thing before, but this is the worst,” declared Dad.

“All on account of the Pony Rider Boys,” piped Stacy.  “Miss Nature is determined to give us our money’s worth in experience.  I’ve had mine already.  She can’t quit any too soon to suit me.”

After a time the guide crept out, his ears keyed sharply to catch warning sounds from above.  Nance had been out but a moment when he darted back under the protecting ledge.  He was just in time.  A giant boulder struck the earth right in front of their place of refuge.  From that moment on no one ventured out.  About an hour before daylight, the storm having lulled, the failing boulders coming down with less frequency, all hands sank down on their wet blankets one by one, and dropped off to sleep.

When they awakened the day had dawned.  The sun was glowing on the peaks of Pluto Pyramid and the Algonkin Terraces far above them on the opposite side of the gorge.  Tad Butler was the first to open his eyes that morning.  He sprang up with a shout.

“Sleepy heads!  Turn out!”

Dad was on his feet with a bound.  Then came the Professor, Ned and Walter in the order named, with Stacy Brown limping along painfully at the rear.

“How do you feel this fine morning?” glowed Tad, nodding at Stacy.