On the drag, we were seeing a lot of overlapping cloven-hoof sign, like combinations of the alphabet's last four letters. Agents have found sign of people crawling across drags on their hands and knees (long, chutelike impressions), and sign of people tiptoeing across drags (shoe-tip abbreviations), and sign of people walking across drags backward in socks (blunted images, kicked soil revealing the true direction of travel). Someone once walked across a drag on his hands (profound, torqued handprints); the man was followed from the drag to a railroad siding, where the prints transformed themselves into elongate gouges in the embankment stones: running hard, he'd jumped a freight. Sometimes, illegal immigrants will survey drags until they find a particularly rocky stretch and cross there, stepping only on stable rocks, as if they were fording a stream. If yielding terrain frames the rocks, they leave almost no sign.
Ideally, a tracker will find fresh prints on a drag, follow them until he can establish a line of travel, and radio in the group's drag coordinates, its heading, and its tread profile. Then another agent will cut the group on a drag some miles north or northeast-all the sheltering towns and safe houses and freight tracks and pickup points lie that way-and either catch it or radio in a revised line, allowing a third agent to leap up to the group. In practice, it's often impossible to categorically identify a group, establish a line, or get a forward cut.
Because the surest way to identify a group is by its distinct assembly of tread patterns, trackers use a lexicon of soles: super chevron, racetrack, wishbone eight ball, propeller, Tetris, basket weave, Kmart special, rifle sights, Flintstones, hourglass, running w, matchstick. When I was out with McCarson, the radio regularly issued sole descriptions: a "diamond-within-a-diamond heel with an instep logo," an "island running w with a slash in the middle and a fine line," a "beetle pincer in the toe." The increasing complexity of sneaker-sole designs frequently creates neologisms. Regions, and sometimes stations, have their own dialects: a sole dominated by lugs in the shape of a z is a "zebar" in Brackettville and a "zorro" in Del Rio.
We cut a blank stretch for a while. "It's gonna be a little quiet," McCarson said. "We haven't had much moon." The moon is a prime instrument of navigation, because it illuminates without stark exposure. (Illegal immigrants also use the sun, stars, and diverse landmarks.) A few minutes later, McCarson stopped the truck. "Well, we got some crossers," he said.
The prints were shallow and had been scrambled by super-imposition; it took McCarson about thirty seconds to disentangle the tread designs and stride lengths and foot sizes. I couldn't find a discrete print. "Group of five," he said: running w, matchstick, heavy-lug boot, fine wire mesh, star-in-the-heel waffle. "They were here last night. They're fresh, but they're not smokin'-hot fresh. When the ground is retaining moisture like this, and you don't have much wind, the sign can hold its shape for a long time. But I see a little better color in our prints than in theirs." Foot pressure, concentrating moisture in the soil, darkens prints; the clock of evaporation steadily lightens them. I couldn't see any color difference. "They could be anytime last night," McCarson said. "And we've had the correct amount of moisture over the correct amount of time to make the ground about like concrete, so they're not leavin' much sign."
If drag prints aren't decisive, trackers examine a group's sign along the first stretch of trail, wary of the corrosive or stabilizing effects of weather and terrain-hilltop wind withers prints; damp arroyos embalm them-and noticing things like insect crossings and preservative soil composition and raindrop cratering. Every left-behind object is a potential timekeeper. There are rare, unambiguous tokens: jettisoned cans of beans that ants haven't yet noticed, sunlit Kleenex still clammy with mucus, fresh bread crusts on a hot, clear day. But most often agents encounter noncommittal objects-desiccated bread crusts in full sun which could be two or ten hours old.
Swinging the shepherd's cane he uses as a tracking aid, Mc-Carson started cutting. Just beyond the drag was a strip of mesquite scrub, and then freight tracks on a high gravel embankment. In the scrub, the prints disappeared abruptly, as if the group had been choppered out. But McCarson read a carnival of sign through the scrub and followed a sequential displacement of gravel up the embankment. He pointed to a railroad tie and kept going. Possessed by the live trail, he couldn't pause to explain.
I sat down and studied the tie. It looked like every other tie. I began shifting position relative to the obfuscated sun. Eventually, three stacked ws of discoloration, collectively the size of a half-dollar, shimmied into view.
On the other side of the tracks, McCarson was standing in front of a fence, methodically locating the crossing point with his cane. Beyond the fence, the mesquite gave way to scrofulous pastureland. The wind picked up and a stop-start drizzle began. Any moderately heavy rain melts sign, toughens vegetation, and hardens the arid earth. McCarson walked along the edge of the scattershot grasses for a while, hesitant, and then accelerated.
He was mainly scrutinizing stalks of buffalo grass and curly mesquite grass and king ranch bluestem. The group had pressed the grasses forward. Now at a vestigial angle, the stalks reflected the light more directly, like opened compact mirrors, whitening it. Mc-Carson described this effect later; for the moment, my experience remained completely secondhand-even after he had amplified the sign by walking right over it, my glances fell nowhere.
I could see that moisture had strengthened and limbered up the grasses: instead of breaking and lying inert after receiving their foot-blows, which makes for the brightest reflection, they had been rebounding in slow motion for many hours, and had nearly regained their posture, although adhering rain droplets now pulled them down like sinkers and a jittery wind ceaselessly repositioned them. Under the dingy, dropped-down clouds, the reflective power of the grass was negligible, and the rainy light shrank the color differences.
The mesquite thickened; the grasses faded out; the static of drizzle hardened the ground and corroded the sign. "This is some tough cuttin'," McCarson said, neutrally. The terrain was too stingy for prints, but the walkers had scored the earth with the soles of their shoes, and McCarson was following the scuff marks, which were often the size of fingernail clippings and about as much lighter than the surrounding earth as a No. 2 pencil is lighter than a No. 1.
In cow shit or ant-processed dirt or hoof-crushed earth, Mc-Carson found fractional footprints. Largely dismantled by drizzle and generally separated by a quarter mile, they were about the size of suit buttons. For retracing purposes, he marked them by scraping a line in the adjacent dirt with his cane. He kept moving and held the silence of his concentration, but there was satisfaction in the absoluteness of the stroke and the granular conclusive sound itself: shhhick!
The ground was still hardening; the rain-erosion got worse. McCarson slowed, occasionally bending down a little and poking something diagnostically with his cane, but he never crouched and almost never came to a full stop.
"Well, we're just suckin' on the hind teat on this one," he said. A minute later he said, "Oh, by God, that's them!" and accelerated down an alley of spectral sign. Five minutes later, he slowed again. "The odds of following these five are pretty slim in these ground conditions," he said. "We're losin' so much time just tryin' to stay on the sign, we won't really catch 'em unless we take a risk."
So we held their line and walked fast down numberless, seemingly uninstructive trails. McCarson's trail choices appeared to be random, but he was sensing the path of least resistance, relating it to the group's hypothetical line of travel and behavioral tendencies, and occasionally seeing candidate sign. A few times, where the ground turned permissive, we swept perpendicularly back and forth, hoping for trapped sign. After fifteen minutes, McCarson said he was beginning to doubt the trueness of the line.