Debris rained down Saturday over hundreds of square miles of Texas and Louisiana, smashing a rooftop, splashing into a reservoir and sending emergency crews on a far-flung hunt for bits of what was once space shuttle Columbia.

• Map: Witness/Debris Sightings

Across the city of Nacogdoches and the surrounding region of pine forest, residents found chunks of debris. A small tank rested on a runway. A steel rod with silver bolts was roped off behind yellow police tape in a yard. A piece of metal rested in a bank parking lot.

Authorities urged the public to report any debris but not touch it for fear of contamination from toxic substances. The Army sent in helicopters and soldiers to locate and guard bits of wreckage, which could be pivotal in determining the cause of the disaster.

In Hemphill, near the Louisiana state line, hospital employee Mike Gibbs reported finding what appeared to be a charred torso, thigh bone and skull on a rural road near what was believed to be other debris. Billy Smith, an emergency coordinator for three East Texas counties, confirmed the find.

"I wouldn't want anybody seeing what I saw," Gibbs said. "It was pretty gruesome."

The Columbia broke apart in flames 200,000 feet over Texas, killing all seven astronauts just minutes before they were to glide to a landing in Florida.

Debris has been tracked in a 500-square-mile area but could be spread over a region three times that, said James Kroll, director of the Emergency Geospacial Mapping Center at Stephen F. Austin State University in Nacogdoches.

As authorities rushed to secure pieces of the shuttle, residents gathered to get a glimpse.

"Everybody's treating this like it's an alien crash," said Phillip Russell, 17.

Jim Stutzman of Nacogdoches -- 135 miles northeast of Houston -- found a 9-inch long, 2-inch wide piece of metal in his yard. "It has heat burns, melted metal and some of the grass burned into it when it fell," he said.

Jeff Hancock, a 29-year-old dentist, said a foot-long metal bracket smashed through the roof of his office.

"It's all over," said James Milford, owner of Milford Barber shop in downtown Nacogdoches. "There are several little pieces, some parts of machinery."

Dozens of residents gathered in front of Rice High School, about 40 miles southeast of Dallas, to look at what appeared to be a charred piece of tile from the space shuttle. The area around the piece was blocked off with tape.

"It's just kind of an event that doesn't happen every day," said Rhonda Martin, 32, of Kemp. "It's going to go down in history." Martin held her toddler son while her husband took photos.

Behind a bank in Nacogdoches, flowers were laid out -- including seven pink roses -- in a makeshift memorial as residents gathered around a taped off area that contained a 3-by-3 piece of metal.

Ed Rohner, Nacogdoches airport manager, said some type of tank ended up on a runway, and debris was scattered along the airport entrance road.

Cherokee County Sheriff James Campbell said debris was reported to have fallen around the towns of Jacksonville, Palestine, Rusk and Athens in east Texas.

"We've had people bring pieces of it up here to the office," he said. "We certainly want to discourage that.

Debris found in San Augustine County about 140 miles northeast of Houston included a charred astronaut's patch and a flight helmet.

Debris also scattered in western Louisiana, including a smoldering bundle of wires in a Shreveport front yard and pieces that reportedly dropped into Toledo Bend reservoir on the Texas border, threatening water supplies.

"I heard the piece coming down through the air. It sounded like it was fluttering," said Elbie Bradley, 69, who was fishing on the reservoir.

Two F-16s from the Naval Air Station Joint Reserve Base in Fort Worth were dispatched to Tyler to map the debris field.

Helicopters and soldiers from Fort Hood in central Texas were also dispatched, a spokesman said. Members of the National Guard were protecting the debris.

Authorities ordered people to stay 100 yards away from the debris because of contamination fears. However, a number of Nacogdoches residents were picking up pieces and turning them in to law enforcement officers.

G.W. Jones, assistant administrator at Nacogdoches Memorial Hospital, said 27 people had come to the hospital seeking information after touching pieces of debris. He had no reports of any adverse effects so far.

"We're telling them to just wash their hands and any other body parts that may have come in contact with the debris," Jones said. "The first thing is not to touch it. If they do, they should contact their local ER or family doctor for any follow up."

Shuttles have long used a chemical called hydrazine to run their auxiliary power units. Hydrazine, a colorless liquid with an ammonia-like odor, is a toxic chemical and can cause harm to anyone who contacts it.

Much of the area where debris has been reported lies in the Piney Woods timber region of east Texas, which is rugged and densely wooded in places. The Texas Forest Service was helping local officials plot debris locations on a map.

NASA set up telephone number for people who find debris to call: 281- 483-3388.