t's the trench for?" asked Jack, who had been busy with the three
tents, for they had decided on Zeb's advice not to use the old
roofless shack to sleep in.

"No tellin' what kind of varmints, from skunks to rattlers, ain't
makin' a hotel out of it," he said, "not to mention tarant'las, which
has a most unpleasant bite, and scorpions and centipedes that ain't
much nicer bedfellows."

This was quite enough to make the boys willing, nay anxious, to set up
the waterproof silk tents.

"What's the trench for?" asked Zeb. "Well, if it should come on ter
rain in ther night it'll keep us dry to have a trench round each
tent."

"Rain!" exclaimed Tom incredulously. "Why, it doesn't look as if it
ever rained here."

"It doesn't, not more'n about two inches a year," rejoined Zeb, "but
when it does you'd think ther flood gates uv heaven had been ripped
wide open."

"Do you think it will rain to-night?" asked Jack.

"It looks uncommon like it," answered Zeb. "See them clouds off there
yonder?"

He pointed to some heavy-looking masses of vapor hanging above a dim
range of saw-backed mountains off to the east.

"In my opinion they're plum full of rain," he said.

"In that case we'd better get ready with the trenches," declared Jack.
He picked up one shovel and gave another to Tom. The latter made a wry
face but said nothing. Tom liked hard work no better than most boys,
but he realized that the work had to be done, and so tackled it with
the best grace he could.

Secretly he wished himself to be with Dick Donovan, who had been
assigned to go fishing to see if he couldn't get "something" fresh for
supper. The professor, as usual, was off somewhere collecting
specimens.

But the task of digging the trenches was not as arduous as it had
appeared. The sand was soft and yielding, and the shovels made rapid
work with it. Soon a fairly deep trench was dug round each of the
temporary shelters.

By the time the lanterns had been filled, and Zeb had cut a goodly
stack of mesquite wood, everything was ready to begin preparations for
supper.

"We'll have a blow-out to-night," said Zeb. "Canned salmon, beans,
crackers, cheese and canned fruit, but don't expect to get that right
along. I've lived on beans and bacon for six months in this very neck
of the woods, and thought myself lucky to get that."

"Hullo!" came a cry from the direction of the river.

"There's Dick!" exclaimed both boys, and then as the young reporter
came