“Where?  At Sunken Valley?”

“The place is not mentioned.”

“Lacy write it?”

“Yes; at least he signed it; there’s a message there about cattle, too, but I can’t quite make it out.”

“Well, we don’t care about that.  If Lacy aims to meet Mendez to-night, he ought to be along here soon after nightfall.  How’d it do to hide in these sand-hills, and wait?”

“We can do that, Dan, if we don’t hit any trail,” said Westcott, leaning over, his hand on the other’s knee, “but if we can get there earlier, I’d rather not waste time.  There’s no knowing what a devil like Mendez may do.  Let’s take a scout around anyhow.”

They started, the one going east, the other west, and made a semicircle until they met, a hundred yards or so, south of the spring, having found nothing.  Again they circled out, ploughing their way through the sand, and all at once Brennan lifted his hand into the air and called.  Westcott hurried over to where he stood motionless, staring down at the track of a wagon-wheel.  It had slid along a slight declivity, and left a mark so deep as not yet to be obliterated.  They traced it for thirty feet before it entirely disappeared.

“Still goin’ south,” affirmed the marshal, gazing in that direction.  “Don’t look like there’s nothin’ out there, but we might try—­what do you say?”

“I vote we keep moving; that wagon is bound to leave a trail here and there, and so long as we get the general direction, we can’t go far wrong.”

“I reckon you’re right.  Come on then; let’s saddle up.”

It was a blind trail, and progress was slow.  The men separated, riding back and forth, leaning forward in the saddles, scanning the sand for the slightest sign.  Again and again they were encouraged by some discovery which proved they were on the right track—­the clear print of a horse’s hoof; a bit of greasy paper which might have been tied round a lunch, and thrown away; impresses in the sand which bore resemblance to a man’s footprints; a tin can, newly opened, and an emptied tobacco-pouch.  Twice they encountered an undoubted wheel mark, and once traces of the whole four wheels were plainly visible.  These could be followed easily for nearly a quarter of a mile, but then as quickly vanished as the wagon came again to an outcropping of rock.  Yet this was assured—­the outfit had headed steadily southward.

This was desperately slow work, and beyond that ridge of rock they discovered no other evidence.  An hour passed, and not the slightest sign gave encouragement.  Could the wagon have turned in some other direction?  In the shadow of a sand-dune they halted finally to discuss the situation.  Should they go on?  Or explore further to the east and west?  Might it not even be better to retrace their way to the springs, and wait the coming of Lacy?  All in front of them the vast sand plain stretched out, almost as level as a floor.  So far as the eye would carry there was no visible sign of any depression or change in conformity.  Certainly there was no valley in that direction.  Beyond this dune, in whose shelter they stood, there was nothing on which the gaze could rest; all was utter desolation, apparently endless.