Information about a known mudslide area is available for years but perhaps not to the general public.
Insurance against this is available for $1000 (a year, I guess) on a house costing $300K. I guess your heirs will collect on this.
I don't know if the ins. companies advertised this ins for that area.
Realtors may not know and probably do not want to know about this info, which is bad for business. I don't know if house prices just downstream of this hill were lower than average.
Now that you all know this, what would you have done two months ago?
Roll the dice?
Stay at a motel during excessive rainfall?
Sell your house immmediately?
A retaining wall for 15M cubic feet of soil was probably out of the question, even for these guys
and is now unnecessary.