That expressed their nature.  They were the orchids of the summer canyon.  They stood up everywhere starlike out of the green.  It was impossible to prevent the mustangs treading them under hoof.  And as the canyon deepened, and many little springs added their tiny volume to the brook, every grassy bench was dotted with lilies, like a green sky star-spangled.  And this increasing luxuriance manifested itself in the banks of purple moss and clumps of lavender daisies and great clusters of yellow violets.  The brook was lined by blossoming buck-rush; the rocky corners showed the crimson and magenta of cactus; ledges were green with shining moss that sparkled with little white flowers.  The hum of bees filled the air.

But by and by this green and colorful and verdant beauty, the almost level floor of the canyon, the banks of soft earth, the thickets and the clumps of cotton-woods, the shelving caverns and the bulging walls—­these features gradually were lost, and Nonnezoshe Boco began to deepen in bare red and white stone steps, the walls sheered away from one another, breaking into sections and ledges, and rising higher and higher, and there began to be manifested a dark and solemn concordance with the nature that had created this rent in the earth.

There was a stretch of miles where steep steps in hard red rock alternated with long levels of round boulders.  Here one by one the mustangs went lame.  And the fugitives, dismounting to spare the faithful beasts, slipped and stumbled over these loose and treacherous stones.  Fay was the only one who did not show distress.  She was glad to be on foot again and the rolling boulders were as stable as solid rock for her.

The hours passed; the toil increased; the progress diminished; one of the mustangs failed entirely and was left; and all the while the dimensions of Nonnezoshe Boco magnified and its character changed.  It became a thousand-foot walled canyon, leaning, broken, threatening, with great yellow slides blocking passage, with huge sections split off from the main wall, with immense dark and gloomy caverns.  Strangely, it had no intersecting canyon.  It jealously guarded its secret.  Its unusual formations of cavern and pillar and half-arch led the mind to expect any monstrous stone-shape left by an avalanche or cataclysm.

Down and down the fugitives toiled.  And now the stream-bed was bare of boulders, and the banks of earth.  The floods that had rolled down that canyon had here borne away every loose thing.  All the floor was bare red and white stone, polished, glistening, slippery, affording treacherous foothold.  And the time came when Nas Ta Bega abandoned the stream-bed to take to the rock-strewn and cactus-covered ledges above.

Jane gave out and had to be assisted upon the weary mustang.  Fay was persuaded to mount Nack-yal again.  Lassiter plodded along.  The Indian bent tired steps far in front.  And Shefford traveled on after him, footsore and hot.