Very good question about the cabin heat.
Its a simple shroud around the muffler that vents the air into the cabin. Dangerous as all get out if there is a carbon monoxide leak which just might have been what caused this incident. Atleast that would be consistent with the comments about high noise levels, the probable inverted attitude at impact, the engine developing power but apparently not full power and the pitch control possibly at cruise instead of climb.
Another possibility is bird strike incident.
Recapitulation of Search:
Flight was purely a pleasure flight; it was not to scope out flat racing sites.
He said he would follow a particular road and apparently did so only deviating to take a very scenic route to one of the 14,000 foot peaks he had not yet climbed but was one he intended to climb.
CHP sighting is consistent as to time and place.
Ranchhand Brawley at hill top cell phone conversation with his girlfriend was familiar with the plane and claimed to have seen it heading for Mud Flat near Hawthorne but this appears now to have been given too much weight by the searchers.