Adobe Water Tower

An adobe water tower?!? I've never heard of such a thing. I've been in Hillsboro countless times, but have never seen this before. I wish I could inspect it up close, and maybe go inside. Even though I have a picture of it, it's hard to believe it really exists. Surely there's a wooden framework inside the adobe? I mean, most large adobe structures require buttresses to keep them from cracking. Adobe can easily support the weight of the water (8000 pounds or so), but if the tower was even slightly out of plumb, the adobe would crack.

The tower is evidently pretty old -- most of the original plaster has fallen off, the wooden beams at the top are rotting, and water is eating into the adobe in a couple of spots. This tower deserves to be placed on a register of historical structures.