All of them wore the broad, leather-banded sombreros of the plainsmen except Professor Wintergreen, who had invested himself in a gigantic pith sun-helmet, from beneath which his spectacled countenance peered out, as Ralph said, "Like a toad peeking out from a mushroom." For the rest, the boys wore leather "chaps," blue shirts open at the neck, with loosely knotted red handkerchiefs about their throats. The latter were both to keep the sun off the back of their necks and to serve as protection for their mouths and nostrils against the dust in case of necessity,--as for example, when they struck a patch of burning, biting alkali. Of this pungent stuff, they had already encountered one or two stretches, and had been glad to muffle up the lower part of their faces as they rode through it. As for Coyote Pete, those who have followed his earlier experiences are pretty familiar with that redoubtable cow-puncher's appearance; suffice it to say, therefore, that, as usual, he wore his battered leather "chaps," faded blue shirt, and his big sombrero with the silver stars affixed to the stamped leather band. In a holster he carried a rifle, as did the rest of the party, as well as his well-worn revolver. The others had provided themselves with similar weapons, although theirs glittered in blatant newness beside Pete's battered, but well-cleaned and oiled, "shootin' iron." While they are pressing onward, with the Hachetas lying like a dim, blue cloud far behind them, let us tell the reader something about the quest that brings our party into the midst of this inhospitable place. As readers of "The Border Boys on the Trail" know, Professor Wintergreen had accompanied Jack Merrill and Ralph Stetson from Stonefell College, some weeks before, to spend a vacation on the Agua Caliente Ranch, belonging to Jack's father. The professor, as well as being on a vacation, was in a sense on a mission, for he bore with him the commission of a well-known institute of science in the East to investigate some of the mesas of this part of the world, and also to procure relics and trophies of the vanished race that once inhabited them, and accurate measurements of the strange formations. Since their arrival at the ranch, some weeks before, events had so shaped themselves as to render the immediate undertaking of his mission impossible. The descent of Black Ramon de Barros on the ranch, as we have related, and the subsequent abduction of the boys to the old Mission across the border, had so fully occupied their attention, that all thought of the professor's errand had been lost sight of.