my father explained it to me:
mesivta of greater los angeles – calabassas (which is in the valley technically, but if you live in calabassas, you say you live in clabassas, not san fernando valley.)
los angeles mesivta – the high school of the boys’ cheder. it’s in the city. and chassidish, mostly (i used to pass boys going there on my way to school = mortifying!!!! but i always used to wonder what the goyim must’ve been thinking, seeing a boy and girl coming down the street towards each other, but as soon as they notice each other, the girl starts walking in the street and the boy hugs the walls on the other side of the sidewalk, both of them pointedly looking everywhere else but at each other. it alway made me laugh. that was before i walked in the alleys…)