Additionally, isn't it most likely that your region is heavily taken by IPAs because it is near the major hops growing region? It may be one of the few examples of a local ingredient influencing a regional palate and maybe even culture.I suspect there's something to this. I want there to be something to this. And yet, how's that old saw go?--correlation is not causation. Historically, that is, before humans developed the tech to ship ingredients cheaply around the world, the relationship between ingredients and tastes was a mutually-enforcing cycle. People brewed with what they had access to, and that seems to have inclined them to like what they had brewed. So they liked beer made with local ingredients. The pattern is so strong that Alan's thesis has the aroma of truth.
If it is true, the connection must come from brewers, not consumers--many of whom are totally ignorant about where hops come from. (It's changing, but I'm regularly startled when I'm chatting with someone local who doesn't realize where the hops are grown.) Of course, brewers do know. And it is the hard-hearted Northwestern brewer who did not take joy and pride in using Cascade, Willamette, Chinook, and Mt. Hood hops, or promoting beers made with these hops, or brewing beer that took extra advantage of them.
(Random sidebar. I first started brewing in Wisconsin in the early 90s. It was a bit bereft there at the time beer-wise, and I wanted me some tasty NW-style ales. At the homebrew shop on State Street in Madison, the local shop owner helped us--it was the beeronomist--assemble our ingredients. His standard first-recipe kit utilized Willamettes, which he rendered WILL a mets. We said, no, it's pronounced wuh LAMB its; we know, we're from Oregon. [There was a town just south of Madison called Oregon, pronounced bizarrely, but I'll avoid further sidebars to the sidebar.] To our pleasure, he was really impressed to know we came from the craft brewing motherland. Oregonians love validation.)
Even in the early days, when the craft bedrock was heavily built on amber ales and hefeweizen, hoppy ales were a substantial vein--one I mined early and often. The super-hopped ale subculture was already rolling by the late 1980s from San Francisco to Seattle even when there was no commercial impetus. It took the market more than a decade to catch up to what the brewers were doing.
There's another dimension to the local connection thesis. IPA's ascent to full dominance in the Pac NW didn't really start until the mid aughts. That coincided with the rise of fresh hopped ales, which put a spotlight not only on the hops, but their point of origin, just an hour away from most Oregon breweries. Indeed, Oregon has had an advantage even over Washington on this score--not only are the hops closer to most breweries, but the farms are smaller and were quicker to work with local brewers. That relationship is unique in the world of brewing. It's not a definitive argument, but it's another piece of circumstantial evidence.
Still, we have only smoke and no fire, correlation and no obvious case for causation. (There is evidence to the contrary, too. For one thing, Northwesterners seem to love strong flavors. That San Francisco to Seattle corridor also happens to be where good coffee started. Further, it seems likely that other regions will also quickly develop the Northwest's appetite for IPAs even where no hops are grown locally.) So Alan, I think what you say is true, but I can't quite build an airtight case.