From my experience (back in the high school days, I don't dabble anymore, so thi...

From my experience (back in the high school days, I don't dabble anymore, so this is somewhat dated but not massively so) most high-quality marijuana in Washington comes from north of the border. While Washington has been fairly lax on consumers (as you point out), they have not been lax on growers, and definitely not growers on industrial scales [0][1][2] (though 2 does say they are seeing more local growing). Also, smuggling from BC is fairly sophisticated and most smugglers are doing it in both directions and have some sophistication. They generally don't just try and drive it through a manned checkpoint. Helicopters have been known to be involved [3][4][5]. It is not uncommon for BC marijuana to be smuggled in to Washington and exchanged for cocaine that came to Washington from California, and came to California from Mexico. When I was on a grand jury a couple of years back we saw numerous indictments involving this kind of thing (i.e. smugglers from Canada bringing down pot/ecstasy and exchanging it for cocaine and heroin in Washington).