John Amoroso, right, of the Kern County Search and Rescue, uses radio to communicate Thursday with other search and recovery teams climbing in the Inyou Forest to the crash site of adventurer Steve Fossett near Mammoth Lakes, Calif. At left is search team member Travis Deardorff.

Mammoth Lakes, Calif. ? More than a year after the mysterious disappearance of millionaire adventurer Steve Fossett, searchers found the wreckage of his plane in the rugged Sierra Nevada, along with enough remains for DNA testing.

A small piece of bone was found amid a field of debris 400 feet long and 150 feet wide in a steep section of the mountain range, the National Transportation Safety Board said at a news conference Thursday. Some personal effects also were found at the site.

Officials conflicted on whether they had confirmed the remains were human.

“We don’t know if it’s human. It certainly could be,” Madera County Sheriff John Anderson said late Thursday, hours after the leader of the NTSB had said the remains were those of a person. “I refuse to speculate.”

Asked about the sheriff’s assessment of the physical evidence, NTSB spokesman Terry Wiliams reaffirmed NTSB acting Chairman Mark 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.

Fossett, the 63-year-old thrill-seeker, vanished on a solo flight 13 months ago. The mangled debris of his single-engine Bellanca was spotted from the air late Wednesday near the town of Mammoth Lakes and was identified by its tail number. Investigators said 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.

NTSB investigators went into the mountains Thursday to figure out what caused the plane to go down. 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.

Search crews and cadaver dogs scoured the steep terrain around the crash site in hopes of finding at least some trace of his body and solving the mystery of his disappearance once and for all. A sheriff’s investigator found the 2-inch-long piece of bone.

The remains are enough for a coroner to perform DNA testing, NTSB acting Chairman Mark Rosenker said.

“Given how long the wreckage has been out there, it’s not surprising there’s not very much,” he said.

Fossett vanished on Sept. 3, 2007, after taking off from a Nevada ranch owned by hotel magnate Barron Hilton. The 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. A judge declared Fossett legally dead in February. For a while, many of his friends held out hope he survived, given his many close scrapes with death over the years.

The 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 in the Inyo National Forest. Investigators said animals might have dragged the IDs from the wreckage while picking over Fossett’s remains.