By Pauline Arrillaga
The Associated Press

DOUGLASS, Texas - On horseback and in four-wheel-drives, hundreds of law officers and volunteers tromped through piney woods, over pastures and through swamps Sunday, looking for pieces of Columbia that could explain what brought the shuttle down.

Pieces as small as a quarter and as big as a pickup were being secured and will eventually be analyzed at Barksdale Air Force Base next door in Louisiana.

Experts will try to reassemble sections of the shuttle to figure out how it broke apart and why. Before the shuttle went up, every piece was numbered and carefully cataloged.

Through thick woods that are home to wild hogs and bobcats, 75 volunteers and law officers carried out their hunt near Hemphill on the Louisiana line. About 40 feet into the forest, a searcher shouted, "Hold!" when he spotted a chunk of metal dangling from a limb.

A volunteer marked it with a red flag.

Not too far away, in the community of Douglass, an 18-inch piece of what appeared to be duct piping put a dent in the roof of the school. Debris was also found near the pitcher's mound of the baseball field and the track. Little orange flags marked every piece.

"We're just fortunate no one was injured by it," Principal Jay Tullos said as a technician carrying a remote Global Positioning System satellite backpack plotted some two dozen pieces of shuttle debris that rained down on the 20-acre campus.

The GPS mapping is a key of the investigation. By pinpointing the location of each piece, scientists can figure out the sequence in which the shuttle broke up.

Douglass, a farming and ranching community about 150 miles northeast of Houston, is one of hundreds of evidence sites in a multistate debris field dotted with creeks, lakes and reservoirs.

The search for the possibly thousands of pieces sprinkled over hundreds and hundreds of miles is an awesome undertaking.

The search is concentrated in the Piney Woods of East Texas, a region that is home to four national forests covering almost 700,000 acres of land. There are patches of pine and oak and large swaths of farm land and cattle pastures.

With two nearby reservoirs that together cover about 300,000 acres, the area is a haven for boaters and anglers. But it makes the job facing Columbia recovery teams that much more difficult.

"This is forest - dense forest," said James Kroll, director of the Emergency Geospacial Mapping Center at Stephen F. Austin State University in Nacogdoches. His GPS technicians were aiding NASA.

So far the GPS map, focusing just on Nacogdoches County, shows a 100-mile debris field 10 miles wide, he said.

"There is no way to describe how many pieces there are and how spread over the landscape they are," he said. "Ten years from now, folks are going to be walking around the woods and finding stuff."

Constable Micah Hightower of nearby San Augustine reported finding debris "as big as a quarter to as big as a pickup." Some remains also have been recovered in that area, along with a charred helmet and an astronaut's patch.

In Nacogdoches County alone, a 900-square-mile region that is home to 60,000 people, authorities have logged more than 800 reported sightings of debris. Throughout the day, state troopers stood guard alongside two-lane highways, restaurants and ranches to shoo onlookers away from charred wreckage as they awaited teams from NASA to remove the debris.

A state-federal command center that will be staffed by 300 officials from 30 agencies has been set up in the civic center in Lufkin to oversee debris collection, said NASA spokesman Dwayne Brown. Brown said Lufkin was chosen for its central location; it is also home to an FBI office.

Brown said the agencies include the FBI, Federal Emergency Management Agency and the Texas Department of Public Safety.

After the debris is trucked to the air base in Louisiana, 20 engineering experts from shuttle contractor United Space Alliance will examine the wreckage.

Though local officials did not have enough manpower to protect every piece discovered, Kennedy said NASA had provided a list of priorities in deciding what to locate and guard: anything that could contain data or resembles computer circuitry, or potentially radioactive material.