If a stranger fell from a great height onto someone's backyard and started bleeding to death, the person who lives there isn't legally obligated to give help or call for assistance, right? Oh, and said house is in California.
The stash isn't the problem, what will he do with the people in his basement?
You lock that door to the basement and pray to God nobody sees or suspects a goddamn thing.
As for the question, I believe you could be charged with negligence, but if the person dies........who's to know he or she (of whom, fell from the sky) was ever even there?