I live in the west los angeles area and there are some conures that fly over my apartment regularly, maybe even once a day. not a flock of 200 but maybe 50. i assume they are mitreds because that is what everyone says they see around here....EG a friend saw a flock of mitreds in mar vista (near venice beach) which i am guessing is the same flock i see, since I live near there. from my window, however, i can only tell for sure they are conures.
there is also a flock of wild nandays that live about six miles to the west of me, but i think they pretty much stay down there close to ocean.
apparently there is some bush with sticky fruit that grows around here that they like to eat.
further to the north, there is a flock of misfits that has some amazons and blue-headed conures. I am guessing that what is in the above picture, though there might be multiple flocks like this. check this out for some cool stories about the california parrots, especially Tavia:
http://californiaparrots.us/