Thanks for the additional ideas.

Dazbo, one of my favorite memories is approacing Denver from the south and viewing the Front Range down its length. Such power was involved in the making of that huge, knife-edge mass.

I've yet to find an explanation for it.

Becky, I'm off to Google Earth to look at the sandhills of Nebraska.

(In a few weeks I'll be going to Nebraska to see the sandhill cranes. It's a wonderful sight.)