A mix of two concepts:
"LA" is presumably not the Lennox and Addington revered by Avril Lavigne fans worldwide but Los Angeles, a podunk California town which attracts would-be actresses and models from all over. Many have perfect faces.
Conversely, Oakland is a city in the Bay Area in which many who have been priced out of San Francisco by the Silicon Valley rabble and the dot-com bubble have taken refuge. A black man and a rapper, Sir Mix-A-Lot would be
looking for ghetto booty - a booty that is large, round, and bootylicious.
So, presumably,
the best of both worlds.
Seattle-based rapper Sir Mix-A-Lot saw the Oakland girls might not have been
China doll beautiful like the A-list cinema stars from Burbank, but were
particularly endowed in another area.
This phrase, LA face with an
Oakland booty, is talking about a female who has both.