I tried marijuana once. Then repeatedly for between my junior year of high school and sophomore as an undergraduate. It was a phase I went through that help me waste a lot of time, meet a lot people, and learn an enormous amount of slang.
Having not purchased in more than a year, I forgot the absolute lexical fluidity in the drug user's cant so when I was watching my little and his roommate refer to hits from a gravity bong as a swat I was incline to comment.
We've all been on youtube, better yet we've all watched television, even better yet we've all read a newspaper. What these three media all have in common is that they each help to standardize a language and render null dialectical differences. The various forms of Italian in the 1920's could almost be viewed as different language. Today, thanks to mass media influence standard Italian has not only gained a foothold but is massacre-ing regional variants.
The same is widely true across the States, but with some exceptions, specifically drug lingo. I came to learn that swat is a hit from a g-bot common used in the St. Augustine/Jacksonville area of Florida.
On shows like Weeds, Breaking Bad, and any show where a character does drugs, they can say herb, ganja, pot, cannabis because they are widely known. To incorporate a specific area's slang would only serve to confuse and alienate the audience as opposed to simply using a commonly known term like grass. Shows don't even touch on the various strains and grades of drugs (save the occasional chance for a writer to make up some ridiculous name like 'The dank stank' or 'Big Daddy Snowbeast' because its confusing for the housewife tuning in for a story that exciting and sexy because someone mentioned hash.
While regional names for U-turns might die out (except in Minnesota)
the ones for weed, cocaine, and ecstasy will retain their geographic loyalty.
So when in the future when California and New York based telemedia has destroyed all differences in American dialects, you might only be able to tell that someone's from Texas by their word for weed.