Pfertsh plucks a thick wedge of glass from  the  glittering  shards  strewn everywhere and fingers the raised "CCC" -- a maker's mark, he explains, denoting Carl Conrad and Company, a liquor distributor. He notes the fragment's aquamarine hue, created when cobalt, an element used in bottle manufacturing in the late 1800s, is exposed to sunlight over many decades.

Everything points to the questionable practices of the early road-trippers: This particular fragment derives from a 125-year-old Budweiser bottle. "They were drinking and driving," Pfertsh says with a laugh, deducing that it was most likely deposited by wagon travelers hauling goods from a former railroad junction along the Gunnison River.

Pfertsh retrieves another bauble, this one a smooth knob of green glass -- an insulator from a telephone line installed around 1900. From these artifacts, he concludes that we are not standing on a true portion of the Old Spanish Trail but on a latter-day offshoot, known as the Salt Lake Wagon Road. Still, finding these "newer" roads is often as good as finding the original itself. "The old Salt Lake road is reported to have followed portions of the Old Spanish Trail," he explains. "By identifying traces of the wagon road, we have been able to find segments of the much fainter Old Spanish Trail."

Unlike, say, the Oregon or Mormon trails, which received a steady stream of wagon traffic -- their iron-clad wheels incised indelible ruts in the Wyoming steppe -- the Old Spanish Trail was used primarily by pack trains of horses and mules, leaving far less enduring marks. The trail is not a single line of exploration, says Pfertsh, but a tangle of routes that varied depending on the time of year, the types of animals used, the cargo being hauled, the state of tribal relations -- even the traveler's disposition. "It's as much a concept as it is a trail," says Pat Richmond, a Cortez historian and founding member of the Old Spanish Trail Association, a nonprofit group of historians and trail enthusiasts.

Geography is another complicating factor. Particularly in the West, where travel corridors are often constrained by geography (passes through high peaks, say), routes tend to persist over time. This "continuity of travel" means that historical trails often lie within sight -- if not spitting distance -- of modern roads. Sure enough, no more than a half-mile away, a glittering river of traffic courses along U.S. 50.

And, of course, with roads comes the unavoidable clutter of the present: gas pipelines, fiber-optic cables, transmission lines, telephone wires, wind turbines, oil-pumping units. Two massive new energy projects impinge on the trail corridor: BrightSource's Ivanpah Solar Project on the California-Nevada border, and the Silurian Valley Wind Project on the eastern fringes of Death Valley. "People assume that the Mojave is a wasteland and that these green energy projects are without cost. But a proper accounting of the cultural and environmental resources that stand to be lost has not happened," says Liz Warren of the Old Spanish Trail Association. "This project will bring an aura of modernity that is completely out of line with the trail and this landscape."

The route of a historic trail may be altered slightly, according to the National Trails System Act, "to avoid difficult routing through subsequent development ... or (offer) a more pleasurable recreational experience." But that raises important questions. How much, for example, can a historic trail deviate -- detouring around a forest of gas wells or bypassing a 3,000-acre wind farm -- before it is no longer historically meaningful? How does one protect the past when the past is firmly anchored to a changing landscape?

These questions are only beginning to be addressed by the federal agencies involved. "Part of the problem is that the Old Spanish Trail wasn't part of the historic trail system until very recently," says Sarah Schlanger, BLM's former lead manager of the trail. Budget cuts and high turnover at local field offices are compounding factors. Solar, wind and extractive industry projects are proceeding on a much larger scale than land managers have dealt with in the past. "And, as we're learning, it's really hard to 'damp down' the visual elements of alternative energy projects," she says. She also notes what seems to be a core weakness of the National Trails System Act: Though it provides a framework for protecting historic routes, it does not mandate their continuity. "These trails were never expected to provide for 'through-hiking' like the Appalachian Trail or the Continental Divide National Scenic Trail," she says.

The present, pragmatic solution, says Schlanger, is to focus on trail sections in areas little changed since the time of their original use -- areas of high historical integrity. Land managers rank a site's integrity by considering such factors as visible traces of a track, historic artifacts, and the presence of unobstructed views. "It's often very difficult to protect views in the Western U.S., where sightlines can extend for miles," says Barb Pahl, a regional director with the National Trust for Historical Preservation. But it's also the law to attempt to preserve historically significant views. Historic views have been at least nominally accounted for in the 2000 Black Rock Desert Bill, for example, which "serves to protect the integrity of the viewshed" of part of the California emigrant trail in Nevada.
While some trail segments may still reflect the character of the past, the Old Spanish Trail experience of today is largely defined by juxtapositions, by endless sweeps of sage giving way to the glare of solar reflectors or the glow of the Las Vegas Strip. Much has already been lost, and no one knows how much of what remains can ultimately be saved.

"But at the very least, we'll have a better idea of what is out here," says Pfertsh, gazing out over the old road running faintly over the high plateau toward Delta and the snowcapped San Juan Mountains beyond. "We'll have some data to work with, and that's a good start."