From the looks of it, the plane had slammed straight into a mountainside.
"It was a hard-impact crash, and he would've died instantly," said Jeff Page, emergency management coordinator for Lyon County, Nev., who assisted in the search.
Crews with cadaver dogs located a few personal effects amid the mangled metal and a small bone fragment. Search teams planned to hike back out to the site Friday to scour the steep flank for more traces of the missing aviator.
The National Transportation Safety Board said the remains found Thursday were enough to perform DNA tests to determine if they belonged to Fossett.
"We found human remains, but there's very little. Given the length of time the wreckage has been out there, it's not surprising there's not very much," said NTSB acting Chairman Mark Rosenker. "I'm not going to elaborate on what it is."
Madera County Sheriff John Anderson described the finding by one of his lieutenants as an oblong piece of bone, measuring 2 by 1 1/2 inches. Anderson also made a point of saying the bone fragment had not yet been confirmed as human.
"We don't know if it's human. It certainly could be," Anderson told reporters Thursday evening. "I refuse to speculate."
He said it would be sent to a California Department of Justice lab for testing.
Asked about the sheriff's assessment of the physical evidence, NTSB spokesman Terry Williams reaffirmed Rosenker's earlier statement.
"We stick by that. It's human remains," said Williams, who declined to say how the NTSB had arrived at that conclusion.
Meanwhile, California National Guard troops also were scheduled to head to the rugged spot in the Inyo National Forest where searchers located the wreckage of the single-engine plane Fossett was flying when he disappeared more than a year ago. They planned to airlift out the surviving portions of the plane in Blackhawk helicopters so they could be reassembled and examined at a nearby hangar.
Most of the fuselage disintegrated on impact, and the engine was found several hundred feet away at an elevation of 9,700 feet, authorities said.
Fossett, the 63-year-old thrill-seeker, vanished after taking off alone from a Nevada ranch owned by hotel magnate Barron Hilton on a solo flight 13 months ago. The intrepid balloonist and pilot was scouting locations for an attempt to break the land speed record in a rocket-propelled car.
His disappearance spurred a huge search that covered 20,000 square miles, cost millions of dollars and included the use of infrared technology. For a while, many of Fossett's friends held out hope he survived, given his many close scrapes with death over the years. A judge declared him legally dead in February.
The first breakthrough -- in fact, the first trace of any kind -- came earlier this week when a hiker stumbled across a pilot's license and other ID cards belonging to Fossett a quarter-mile from where the plane was later spotted. Investigators said animals might have dragged the IDs from the wreckage while picking over Fossett's remains.
The area, situated about 65 miles from the ranch, had been flown over 19 times by the California Civil Air Patrol during the initial search, Anderson said. But it had not been considered a likely place to find the plane, given what was known about sightings of Fossett's plane, his travel plans and the amount of fuel he had.
Lt. Col. Ronald Butts, a pilot who coordinated the Civil Air Patrol search effort, said gusty conditions along the mountains' upper elevations hampered the early efforts to search by air, as did the small amount of debris that remained after the plane crashed.
"Everything we could have done was done," Butts said.
As for what might have caused the wreck, Mono County, Calif., Undersheriff Ralph Obenberger said there were large storm clouds over the peaks around Mammoth Lakes on the day of the crash.
Fossett made a fortune in the Chicago commodities market and gained worldwide fame for setting records in high-tech balloons, gliders, jets and boats. In 2002, he became the first person to circle the world solo in a balloon.
"I hope now to be able to bring to closure a very painful chapter in my life," his widow, Peggy, said in a statement. "I prefer to think about Steve's life rather than his death and celebrate his many extraordinary accomplishments."
Marcus Wohlsen reported from San Francisco. Associated Press writers Malia Wollan in San Francisco and Scott Sonner in Reno, Nev., contributed to this report.