Reno: Just over a year after the adventurer Steve Fossett vanished after taking off from hotel magnate Barron Hilton's ranch about 112km southeast of Reno, a lingering mystery has been solved with the discovery of the plane's wreckage in the wilds of California's Sierra Neveda mountain range.

The 63-year-old had slammed into a mountainside at about 10,000 feet.

But a larger question remains: What caused such an accomplished aviator to crash in a place he knew well, on a fine September day? Finding the answer may take many months. On Friday, investigators from the National Transportation Safety Board began hauling debris from the crash site by helicopter.

They plan to reassemble the plane at a Sacramento warehouse to look for mechanical failures.

Gathering archival weather records, including winds, clouds and turbulence for the day of his flight, also is not simple, officials said. With luck, radar data will help determine Fossett's path and pinpoint the time of the crash.

For now, though, investigators can only speculate.