New World metallurgy

I'd heard it proposed that the presence of so much native copper in Michigan, and trading so widespread, that there was no great pressure to learn smelting. Tin ores are quite scarce, so bronze wasn't going to be made locally north of Mexico. Meteoric iron could be found, of course, and seems to have been used here and there.

South, though: Jonathan Hall's post is quite extensive, and if he's correct it looks like Peru had an impressive metallurgical culture, which spread north into Mesoamerica; but apparently the trade didn't go further north into the modern USA. The absence of tin would explain why nobody bothered to try to smelt bronze, and the easy availability of native copper removes the need to smelt copper, but why wouldn't there be some trade? Did the North have nothing the Mesoamericans wanted, or were the desert stretches that great a trade barrier? There's always the coastlines and raft-boats -- unless there really was nothing they wanted.