For years, four trails were an artery for an estimated 400,000 Americans who turned their eyes hopefully toward the Pacific and took Horace Greeley's advice to "Go West, and grow up with the country."

Today these trails -- the Oregon, California, Mormon and Pony Express -- run through busy cities and rustic farmland. Much of their length has been built over, plowed under or swept away, falling victim to the Western growth they started.Now a vast U.S. Park Service project seeks to preserve more than 11,000 miles of the trails across 12 states.

"It's an epic part of our history and a case of people confronting extreme conditions, and in those conditions you see the extremes of human character -- from heroism to absolute depravity," says historian Will Bagley, who has consulted on the trail project. "But it's the response to the conditions that make it not just a great American story but a human story."

The preservation plans include managing important trail sections, erecting markers at important historical sites and trying to cajole private landowners into opening their land to history buffs.

An estimated 60 percent of the four trails now cross privately owned land, according to Jere L. Krakow, superintendent of the Long Distance Trails Office, based in Salt Lake City.

"Our mission is to protect as much of the trail resources as we possibly can, whether that means trail ruts or campsites or graves or even views along the trails," said Krakow. "Part of evoking a sense of the past is to stand someplace that visually has as much of the same historic landscape as it did last century."

The trails began as traditional thoroughfares for the Indian tribes in the area. In the mid-1830s a trickle of emigrants began streaming West in search of cheap land and better lives. The trickle swelled to a flood after 1848 when gold was discovered in California. In the next 12 years, roughly 300,000 men, women and children worked paths westward.

"What you had was a constant stream of people. It was like Grand Central Station," says historian David Bigler, past president of Oregon-California Trail Association, a private group cooperating with the Park Service's Long Distance Trails Office.

"Trying to find a place to camp where there was wood for fuel and water for your animals was a tough job."

Bagley said so much traffic clogged the thoroughfares that the term "trail" was really a misnomer after 1850.

"It really is only properly a trail until the Gold Rush. By then it's a road," said Bagley. "Very, very quickly it is an overland highway, and you get not only immigration but tremendous commerce."

As a result, the American West, which Thomas Jefferson predicted would take seven generations to settle, blossomed during a single lifetime.

"You could come West as a young trapper in the 1830s and live until the turn of the century and see the entire wilderness transformed with major cities like San Francisco, Denver and Salt Lake springing virtually out of nothing," said Bagley.

Meanwhile, the Pony Express Trail linked the new settlers to lives they left behind for a short time before the completion of the telegraph in 1861 and the transcontinental railroad in 1869 made The Pony Express obsolete and diminished the other trails' significance.

Still, several modern highways and interstates trace the route traveled by the West's original settlers.

Krakow's office has identified 434 historically significant sites along the trails it would like to mark in some way, either with plaques, concrete markers and in exceptional cases, visitors centers.

The potential sites include Pony Express stations and barns, ferry launches where emigrants crossed rivers, and the starting points for the four trails in a handful of cities in western Iowa and Missouri and in Nauvoo, Ill.

Krakow said an effort is being made to have the markers make note of the Indian tribes that lived in the area when the emigrants first traveled the trails.

There also are 72 trail segments where Krakow thinks a good number of tourists would be willing to drive, hike or ride horseback along interpretive tours.

The entire project is being done on a shoestring budget of just $311,000 a year to pay three staffers, erect markers and print brochures.

The battle to save the trails from the elements and development is a race against time.

In Grantsville, for example, a private prison is set to be built on top of a stretch of the California Trail.

"When you multiply that across 13 states and thousands of miles, you come to grips that . . . 50 to 100 years from now a lot of it will disappear," said Krakow. "I know that you can't save everything, but I think that we have to do the very best we can."