[CedarDave]

Well, I was going to agree with you -- it would seem that the 20 in/yr.line would be to the east of the 100th. Then I looked up the actual data and it appears the 100th is about right. Now, for green grass, trees and similar aesthetics, you may want a line further east!

http://www.ocs.orst.edu/pub/maps/Precipitation/Total/States/OK/ok.gif

[Rte66]

See, they didn't ask me. Granted, those scrub brush to the west of *my line* are the beginnings of the more arid area, but I suppose I was being too provincial in my POV - considering they mean for the *whole* US.

Over at the 100th, the scrub is even scarcer. The Plains Indians, as opposed to the Civilized Ones, chose to stay just west of that 97.4 line for some reason.