L.A. heroin history

[China white]

I just asked this on a different thread so im sorry about that, but at the time i couldnt figure out how to make a thread. I often read books on what the U.S. heroin scene was like back in the day. Particularly in the 40's and 50's. Back then there were no colombians, mexicans, pakistani's, Nigerians on the us scene(at least that i know of). There were hardly any independents, it seemed like all roads led to new york and families. anyways i wonder at what time did the tar start popping up and how fast it took over because powder is pretty much non existent out west. and why it it took over?was it that much cheaper....or was there really not that much heroin in la in the first place. I ask these questions like maybe someone can add some insight