There are several helo operators that offer training in the mountain
environment there in SoCal. Western Helicopters comes to mind near
Rialto. A couple hours dual in nearly any helicopter in the high
country will give you an insight into the do/don't of mtn flying. Major
difference is in the individual helicopter performance under a given
set of circumstances. I've flown in the Rockies, the Sierras, Cascades,
Andes, Drakensburg and Karoo (So Africa). They all have the same
problems when it comes to flying in the high country.
Ol S&B