[jellybean]

Why is there a dark line running through the crowd??

That's the break where I-70 runs, separating the two big patches of land.

I think it's a shadow from the Arch. Here's pic of the area.

[Charles Henrickson]

I think it's a shadow from the Arch.

I agree with you. That's what I said after further thought a little downthread.

Your photo illustrates perfectly how the shadow of the Arch could fall across that space.