when I lived in California these types of parties were the norm all over the place, even among young people in their early 20s. usually they were lingerie parties, where it was mandatory the women dressed in sexy underwear, masks were optional and couples that attended together often separated later that evening. I suppose some would just call them swingers' parties, but given darkness attached to these types of events it was more like selling your soul type of party. lots of drugs, obscure locations (you had to go to sometimes two places to get the directions to the the actual location of the party). there seemed to be a ring of certain people in the night club industry that selectively chose who would get invited and it was very organized.