Ten miles of travel covered the length of the pass.  It opened wide upon a wonderful scene, an arboreal desert, dominated by its pure light green, yet lined by many merging colors.  And it rose slowly to a low dim and dark-red zone of lava, spurred, peaked, domed by volcano cones, a wild and ragged region, illimitable as the horizon.

The Yaqui, if not at fault, was yet uncertain.  His falcon eyes searched and roved, and became fixed at length at the southwest, and toward this he turned his horse.  The great, fluted saguaros, fifty, sixty feet high, raised columnal forms, and their branching limbs and curving lines added a grace to the desert.  It was the low-bushed cactus that made the toil and pain of travel.  Yet these thorny forms were beautiful.

In the basins between the ridges, to right and left along the floor of low plains the mirage glistened, wavered, faded, vanished—­lakes and trees and clouds.  Inverted mountains hung suspended in the lilac air and faint tracery of white-walled cities.

At noon Yaqui halted the cavalcade.  He had selected a field of bisnagi cactus for the place of rest.  Presently his reason became obvious.  With long, heavy knife he cut off the tops of these barrel-shaped plants.  He scooped out soft pulp, and with stone and hand then began to pound the deeper pulp into a juicy mass.  When he threw this out there was a little water left, sweet, cool water which man and horse shared eagerly.  Thus he made even the desert’s fiercest growths minister to their needs.

But he did not halt long.  Miles of gray-green spiked walls lay between him and that line of ragged, red lava which manifestly he must reach before dark.  The travel became faster, straighter.  And the glistening thorns clutched and clung to leather and cloth and flesh.  The horses reared, snorted, balked, leaped—­but they were sent on.  Only Blanco Sol, the patient, the plodding, the indomitable, needed no goad or spur.  Waves and scarfs and wreaths of heat smoked up from the sand.  Mercedes reeled in her saddle.  Thorne bade her drink, bathed her face, supported her, and then gave way to Ladd, who took the girl with him on Torre’s broad back.  Yaqui’s unflagging purpose and iron arm were bitter and hateful to the proud and haughty spirit of Blanco Diablo.  For once Belding’s great white devil had met his master.  He fought rider, bit, bridle, cactus, sand—­and yet he went on and on, zigzagging, turning, winding, crashing through the barbed growths.  The middle of the afternoon saw Thorne reeling in his saddle, and then, wherever possible, Gale’s powerful arm lent him strength to hold his seat.

The giant cactus came to be only so in name.  These saguaros were thinning out, growing stunted, and most of them were single columns.  Gradually other cactus forms showed a harder struggle for existence, and the spaces of sand between were wider.  But now the dreaded, glistening choya began to show pale and gray and white upon the rising slope.  Round-topped hills, sunset-colored above, blue-black below, intervened to hide the distant spurs and peaks.  Mile and mile long tongues of red lava streamed out between the hills and wound down to stop abruptly upon the slope.