Intentionally left the Anchor Brewery off the list. It was established in 1896 (and your date is wrong for their Anchor Steam beer anyway; it was brought back in 1971 -- that's what happens when you cite wikipedia as a source).
There's no doubt Anchor had a huge influence on the early guys who initiated the microbrew revolution, but it was never a microbrewery in the same sense as these others. Rather, it started out as a long-established brewery that had a number of different incarnations over the past century as it weathered the ups and downs of the brewing industry. There are numerous other smaller regional breweries across the nation that persisted over the years and helped rekindle interest in lesser known beers and the brewing craft, but including all of those in this early microbrew list would be ridiculous. For example, Yuengling had a similar effect on the East Coast, sparking interest in craft brewing in the face of the commercial lite beer dominance by continuing production of a porter and a darker. flavorful lager... but you could never say that Yuengling was a "microbrewery" in the same way that the others on this list are.
Originally Posted by Centropolis
I should say that New Belgium was important in really pushing large quantities of good beer into a 1000 mile swath of the unwashed interior, between the Rockies and the Mississippi or a little further east (although New Belgium didnt cross the Mississippi for years) during the 1990s. I think it's been more of a recent trend that it's been a national beer. Same with Boulevard (1989) and Schlafly (1991). Sam Adams is a big exception to the interior, maybe Sierra Nevada.
The rest of those are important, but didn't tip the scales towards helping tip "backwater" states like Missouri, Iowa, and Kansas into having dozens of microbreweries (or I should say having dozens of breweries once again).
Oh yeah, I realize New Belgium was/is definitely a big player. I just wanted to list some of those very "first movers" who were important to the movement and that persisted.