Former Queens of the Stone Age bassist Nick Oliveri has been charged with four felonies after a tense standoff with a S.W.A.T. team in L.A. last month -- and now faces up to 15 years in prison.

As we previously reported, Oliveri was arrested on July 12th -- after a fight with his girlfriend escalated into a four-hour standoff with police. Oliveri was booked on felony domestic violence -- and after police searched his home, they found a fully-loaded rifle.

But that's not all they found -- according to the charging docs, police also found cocaine and methamphetamines.

Oliveri is charged with two counts of possession of a controlled substance with a firearm, 2 counts of possession of a controlled substance, and one misdemeanor count of resisting, obstructing or delaying a peace officer.