That ravine became a canyon.  At its head it was a dry wash, full of gravel and rocks.  It began to cut deep into the bowels of the earth.  It shut out sight of the surrounding walls and peaks.  Water appeared from under a cliff and, augmented by other springs, became a brook.  Hot, dry, and barren at its beginning, this cleft became cool and shady and luxuriant with grass and flowers and amber moss with silver blossoms.  The rocks had changed color from yellow to deep red.  Four hours of turning and twisting, endlessly down and down, over boulders and banks and every conceivable roughness of earth and rock, finished the pack-mustang; and Slone mercifully left him in a long reach of canyon where grass and water never failed.  In this place Slone halted for the noon hour, letting Nagger have his fill of the rich grazing.  Nagger’s three days in grassy upland, despite the continuous travel by day, had improved him.  He looked fat, and Slone had not yet caught the horse resting.  Nagger was iron to endure.  Here Slone left all the outfit except what was on his saddle, and the sack containing the few pounds of meat and supplies, and the two utensils.  This sack he tied on the back of his saddle, and resumed his journey.

Presently he came to a place where Wildfire had doubled on his trail and had turned up a side canyon.  The climb out was hard on Slone, if not on Nagger.  Once up, Slone found himself upon a wide, barren plateau of glaring red rock and clumps of greasewood and cactus.  The plateau was miles wide, shut in by great walls and mesas of colored rock.  The afternoon sun beat down fiercely.  A blast of wind, as if from a furnace, swept across the plateau, and it was laden with red dust.  Slone walked here, where he could have ridden.  And he made several miles of up-and-down progress over this rough plateau.  The great walls of the opposite side of the canyon loomed appreciably closer.  What, Slone wondered, was at the bottom of this rent in the earth?  The great desert river was down there, of course, but he knew nothing of it.  Would that turn back Wildfire?  Slone thought grimly how he had always claimed Nagger to be part fish and part bird.  Wildfire was not going to escape.

By and by only isolated mescal plants with long, yellow-plumed spears broke the bare monotony of the plateau.  And Slone passed from red sand and gravel to a red, soft shale, and from that to hard, red rock.  Here Wildfire’s tracks were lost, the first time in seven weeks.  But Slone had his direction down that plateau with the cleavage lines of canyons to right and left.  At times Slone found a vestige of the old Indian trail, and this made him doubly sure of being right.  He did not need to have Wildfire’s tracks.  He let Nagger pick the way, and the horse made no mistake in finding the line of least resistance.  But that grew harder and harder.  This bare rock, like a file, would soon wear Wildfire’s hoofs thin.  And Slone rejoiced.  Perhaps somewhere down in this awful chasm he and Nagger would have it out with the stallion.  Slone began to look far ahead, beginning to believe that he might see Wildfire.  Twice he had seen Wildfire, but only at a distance.  Then he had resembled a running streak of fire, whence his name, which Slone had given him.