Out of curiosity, I checked Amtrak.com today to see if perhaps it was offering a Los Angeles-Seattle routing on the Southwest Chief (or the Sunset Limited/Texas Eagle) and the Empire Builder, which would make possible a one-zone Guest Rewards award trip via Chicago.
But no such luck -- turns out the Builder leaves Chicago at 2:15 P.M., whereas the Eagle arrives at 2:14 P.M., and the Chief arrives at 3:20 P.M.