I was driving west from Wounded Knee, SD, towards Scotts Bluff, NE. I was on back road two lanes all day.

Just before sunset, passing through a brief rain squall, I started to note a particular quality of intense color in the sky. Within half an hour, the sky grew into the most amazing show I have ever scene.

I pulled over to the side of the highway and watched and made photographs for almost an hour. During that time, only a handful of other vehicles went by. Nobody but me stopped to watch the show. 

As the sun set, the colors became shockingly vivid.

This is an unaltered photo. This is how it looked.