If in fact the Pilot made some sort of radio call....the content of that call should shed some light on the cause.
There is no CVR installed on the aircraft I am reasonably certain.
Unless a definite mechanical cause is discovered.....there can be but one avenue to look to for an explanation.
The odds of a mechanical failure putting the aircraft on the face of such a steep bluff below the summit....well you figure them out.
I wonder what the weather was like that night.....overcast, no Moon or Starlight to aid in controlling the aircraft.....no surface lighting upon leaving the Ranch Headquarters?
How many EMS Helicopters have been lost in such situations....flying VFR/VMC without NVG's across large expanses of unlit terrain?
More than a few....is the answer to that last question.
It shall be interesting to see what the NTSB reports upon completion of its investigation.