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〃Is that it？〃 Nora stared at the screen in disappointment。 This was the last thing she'd expected： confusing monochromatic patterns like no landscape she had ever seen。
〃It's just the beginning。 The Imager takes infrared emissions and radiometry into account； but that would take too long to explain。 It also looks at the earth in three different radar bands and two polarizations。 Each color represents a different band of radar； or a different polarization。 I'm going to paint each color on to the screen； layering one on top of the other。 This'll take a few minutes。〃
〃And then we'll be able to see the road？〃
Holroyd gave her an amused look。 〃If only it were that simple。 We're going to have to beat the shit out of the data before we can see the road。〃 He pointed。 〃This red is L…Band radar。 It has a wavelength of twenty…five centimeters and can penetrate five meters of dry sand。 Next； I'll add C…Band。〃
A blue color scrolled down。
〃This C…Band has a six…centimeter wavelength； and it can penetrate at most two meters。 So what you see here is a little shallower。〃 More key taps。 〃And here goes X…Band。 That's three centimeters。 Basically； it gives you the surface itself。〃
A neon green color rolled down the screen。
〃I don't see how you can even begin to figure all this out；〃 said Nora； gazing at the distorted swaths of colors。
〃Now I'm going to paint in the polarizations。 The outgoing radar beam is polarized either horizontally or vertically。 Sometimes you send down a beam horizontally polarized； and it bounces back vertically polarized。 That usually happens when the beam encounters a lot of vertical tree trunks。〃
Nora watched as another color was added to the screen。 It was taking longer for the program to paint the image on the screen； obviously； the putational problem was being more plex。
〃Looks like a de Kooning；〃 said Nora。
〃A what？〃
Nora waved her hand。 〃Never mind。〃
Holroyd turned back to the screen。 〃What we've got is a posite image of the ground； from the surface to about fifteen feet deep。 Now it's a matter of canceling out some of the wavelengths and multiplying others。 This is where the real artistry es in。〃 Nora could hear a touch of pride in his voice。
He began typing again； more quickly this time。 Nora watched as a new window opened on the screen； lines of puter code racing as routines were added and deleted。 The remote desert vastness was suddenly covered by a thin web of tracks。
〃My God！〃 Nora cried。 〃There they are！ I had no idea the Anasazi…〃
〃Hold on a minute；〃 interrupted Holroyd。 〃Those are modern trails。〃
〃But this area isn't supposed to have any roads。〃
Holroyd shook his head。 〃Some of these are probably wild horse trails； deer trails； coyote trails； mountain lion trails； maybe even four…wheel…drive tracks。 There was some prospecting for uranium in this area in the fifties。 Most of these tracks you wouldn't be able to see on the ground。〃
Nora slumped back in her chair。 〃With all those trails； how can we ever find the Anasazi one？〃
Holroyd grinned。 〃Be patient。 The older the road； the deeper it tends to lie。 Very old roads also tend to spread through erosion and wind。 The pebbles ancient travelers turned up have been smoothed over time； while new roads are covered with sharper pebbles。 The sharper pebbles backscatter more strongly than the smooth ones。〃
He continued to type。 〃No one knows why； but sometimes dramatic things happen if you multiply the values of two wavelengths together； or divide them by each other； or cube one and take the square root of another and subtract the cosine of your mother's age。〃
〃Doesn't sound very scientific；〃 said Nora。
Holroyd grinned。 〃No； but it's my favorite part。 When data's buried as deeply as this； it takes real intuition and creativity to tease it out。〃
He worked with steady determination。 Every few minutes the image changed： sometimes dramatically； sometimes subtly。 Once Nora asked a question； but Holroyd merely shook his head； brow furrowed。 At times； all the roads vanished； Holroyd would curse； type a flurry of mands； and the roads returned。
Time crawled by； and Holroyd grew increasingly frustrated。 The sweat stood out on his brow； and his hands flew across the keys； hitting them with greater force。 Nora's back began to ache； and she found herself shifting constantly in the cheap chair； trying to find a fortable position。
At last； Holroyd sat back with a muttered curse。 〃I've tried all the methods； all the tricks。 The data just won't put out。〃
〃What do you mean？〃
〃Either I get a million roads and trails； or I get nothing。〃 He got up and went to the refrigerator。 〃Beer？〃
〃Sure。〃 Nora glanced at the clock。 It was seven； but the apartment was still insufferably hot。
Holroyd sat down again； passing her the beer and propping a leg up on the puter table。 A knobby ankle protruded from below the cuff； pale and hairless。 〃Is there anything unusual about the Anasazi roads？ Something that might differentiate them from all these animal trails and modern stuff？〃
Nora thought for a moment； then shook her head。
〃What were the roads used for？〃
〃Actually； they weren't really roads at all。〃
Holroyd pulled his leg from the table and sat up。 〃What do you mean？〃
〃They're still a deep archaeological mystery。 The Anasazi didn't know about the wheel and they didn't have any beasts of burden。 They had no use for a road。 So why they would take such trouble to build them has always puzzled archaeologists。〃
〃Go on；〃 Holroyd urged。
〃Whenever archaeologists don't understand something； they cop out by saying it served a religious purpose。 That's what they say about the roads。 They think they might have been spirit pathways； rather than roads for living beings to travel on。 Roads to guide the spirits of the dead back to the underworld。〃
〃What do these roads look like？〃 Holroyd took a swig of beer。
〃Not much of anything；〃 Nora said。 〃In fact； they're almost impossible to see from the ground。〃
Holroyd looked at her expectantly。 〃How were they built？〃
〃The roads were exactly thirty feet wide； surfaced with adobe。 On the Great North Road it appears that pots were deliberately broken on the road surface to consecrate it。 The roads were dotted with shrines called herraduras； but we have no idea…〃
〃Wait a minute；〃 Holroyd interrupted。 〃You said they were surfaced with adobe。 What exactly is adobe？〃
〃Mud； basically。〃
〃Imported？〃
〃No； usually just the local dirt mixed with water； puddled and plastered。〃
〃Too bad。〃 The excitement left Holroyd's voice as quickly as it came。
〃There's not much else。 When the Great North Road was finally abandoned around 1250； it seems to have been ritually closed。 The Anasazi piled brush on the road and set it on fire。 They also burned all the shrines along the road。 And they burned several large structures too； one of which I excavated a few years ago； called Burned Jacal。 Seems it was some kind of lighthouse or signaling structure。 God knows what they used it for。〃
Holroyd sat forward。 〃They burned brush on the road？〃
〃The Great North Road； anyway。 Nobody has done much research on the other roads。〃
〃How much brush？〃
〃A lot；〃 said Nora。 〃We found large swaths of charcoal。〃
Holroyd slammed down the beer； swivelled in his chair； and began hitting keys once again。 〃Charcoal…carbon…has a very specific radar signature。 Even tiny amounts of it absorb radar。 It has an almost nonexistent backscatter。〃
The image on the screen began to shift。 〃So what we're going to look for；〃 he murmured； 〃is just the opposite of what I've been searching for all this time。 Instead of looking for a particular reflection； we're going to look for a shadow。 A linear hole in the data。〃 He punched a final key。
Nora watched as the image on the screen disappeared。 And then…as a new image scrolled down the screen with maddening slowness…she saw a long； faint； sinuous black line etch itself across the landscape： broken in countless spots； yet unmistakable。
〃There it is；〃 said Holroyd quietly； sitting back and looking at her； his face shining with triumph。
〃That's my road to Quivira？〃 Nora asked； her voic