Yes, believe it or not, this is the '90s. The music and cultural references might trick you into thinking the film takes place in the '50s but we're in the '90s and we're in Los Angeles. The only reason we know it's L.A. is that Marsellus tells Butch to not come back because he's lost his L.A. privileges (because it's apparently a privilege to live in a crowded, polluted, expensive, metropolitan area). There aren't any sprawling shots of the city. Most of the scenes take place inside an interior set.
So the geographic setting of Pulp Fiction isn't all that important. To be honest, though, there is an L.A. vibe; lots of noir films were set in L.A., with its seedy neighborhoods and marginal types of people. If you want a city that suggests shallowness and obsession with pop culture, L.A.'s as good as any.