For those wondering, I just spoke to a good friend who also grew up in the same town and mentioned the traction this post got and he clarified that the roll is actually real, the holder is leftover from when the previous building burnt down decades ago but the property owners replace the roll on it every few years when it inevitibly decays and have been doing so for about 3 generations, hence why it was there when we were kids and still is now, it's just sort of a running joke/"urban legend" for the town.
That's the secret Cap, it is man made lol it's a small indoor stream at the Denver Botanic Gardens.