Nice shot, John! I agree with the others. The lighting could be a little better and some clouds would be nice. For what you had to work with, I think you did great, and this is one of those shots that is more about the content than the technical details. My one suggestion would be this... You said that the sky was clear, right? I would use the channel mixer to bring down the blue levels and darken the sky to give it a more foreboding look. But, that's probably just a personal preference.

Nice find!

Paul