Hell, I dunno... You can't believe anything you read on the internet. You know that. Didn't seem right to me either.
Ok... Here we go:
http://www.washington.org/index.cfm?...ype=530&IDPG=0
THAT one is clearly marked "Official," so we know it's true. From 390 ft to sea level. That being said, the Pentagon, from my memory, is situated at a pretty low elevation relative to the surrounding area. The whole damn place is nothing but a filled-in swamp. I'd say the average elevation is pretty close to barely above sea level.
Is that enough discussion about this?