Article about the report to legislature of 7 areas that have potential to be involved in landslides stopping service once again. Note one or more sites north of LAX.
As has been mentioned elsewhere over the years, maintenance-of-way has become increasingly mechanized and manpower requirements have shrunk dramatically. Also, climate change is a factor.
I remember on an Amtrak trip about 30 years ago when the still ran between Salt Lake and LA, in the Mojave Desert there was a long line of trees along the track fed by drip irrigation. You can see it on Google Maps in satellite view between Kelso and Crucero, CA
This was provided along the Sunset Route through the Palm Springs area by the middle 1990s – in the vicinity of Ramon Road it was thick and heavy enough to block the view of trains from the overhead road bridge.