Agree, a couple of things don't quite gel here. I guess we can discount any doubts about SF's flying abilities. Also, a man of his experience wouldn't have got caught out in a mountain valley.
What intrigues me are two things:
1) if indeed he was looking for a large, flat area to break the land speed record, the Mammoth Lakes area isn't exactly the place to go looking
2) apparently the a/c flew straight into the mountain. Straight. I find it very hard to believe that a pilot of SF's experience would approach a ridge head-on.
All very weird indeed