ver, and they pried away the bowlder that kept Pedro a
prisoner.

Sign of the Mexicans they could not find, save that Sanchez had been
removed from the crevice of the stalactites, (at least he was no longer
there), but whether he had had to fast or not, they could not tell. The
Mexicans evidently knew the cave and they had been near the southern end
of it. Though Long Lester could find no trace of their footprints at
either of the exits they knew, there were doubtless others, and it seemed
the wisest course now to look for them outside. For the boys were still
unwilling to give up the chase.

Reporting back to Radcliffe, they learned, to their amazement, that the
pack burros the Mexicans had left near the northern cave mouth had
disappeared, but where, they could not tell from any sign left on the
charred ground outside.

The Ranger would start a search for them in the DeHaviland, once the fire
was under better control. The Forest Service finds its air service as
useful in keeping track of law breakers as of fires. It would be an
extraordinary thing if the careless camper should escape detection, for
the air men can spy them out as easily as anything. But the fire still
ate angrily through the timber, and would spread in all directions if
left to itself. Fire fighting is sometimes a matter of weeks.

It was a dry summer, and all up and down the Sierras, the Rangers were
kept busy fighting the fires that would break out from one cause or
another. The Service 'planes were all busy.

The five campers were back at fire-fighting headquarters,--and Norris
too,--when Ace had an idea. He and Ted would go in search of the Mexicans
in his little Spanish 'plane. Would Radcliffe let them off the
fire-fighting? He would, though he could not give official sanction to
their plan. It was enough. The two boys were off before he could change
his mind,--to Norris's slight uneasiness and Pedro's envy. (But Pedro was
subject to altitude sickness.)

Sometime, Norris had promised Ted, they would go back into the cave and
look for his fossil. But that could wait.

All that afternoon the two boys curveted over the surrounding
scenery,--careful to keep their distance from the whirlwind of
fire-heated air, for they were flying low. The most minute search failed
to reveal the fire setters, but Ace only set his jaw the more
determinedly.

They returned to sleep twelve hours at a stretch. Aviation is the best
cure yet for insomnia, and nei