Here's an interesting article in the New York Times about a town in Mississippi that is turning their nondescript water tower into a landmark. It dates from the 20s, but really its value is as a piece of vernacular.
Vernacular is a concept that gets a lot of play sometimes. It really just means 'everyday' and its the opposite of post-modern.
The pic above is the oldest building in my hometown, Elk Grove, and the town's own water tower. Elk Grove, like a lot of places around the West, can really only trace its history so far back. Most of it original structures were built quickly, cheaply and ultimately they were temporary. To get an idea of what Elk Grove was – and where it may go – means following its journey into modernity.
Clearly, we need to protect the most amazing of the 20th Century's structures, such as DC's Third Church of Christ Scientist. The complete story, though, requires preservation of the banal as well.