I lived in LA a few years ago, and I remember there being plenty of places to walk in LA (few roads without sidewalks), so long as you don't mind the stares you inevitably get for not being in a car.
That varies tremendously by neighborhood, especially depending on when the neighborhood was built. Most places where the street network was put in before WWII have good sidewalks. Some cities kept at it after the war, but lots of places started treating them as optional or as afterthoughts. In my area, I rarely need a sign to tell when I'm walking across the Pasadena city limits because the sidewalks in Pasadena are much better than the ones in surrounding communities.