Trans-Mississippi was a name of the geographic area west of the Mississippi River<span> during the 19th century.
</span>The geography of this area was inhospitable, dry, rugged, with few trees and extreme weather.The Trans-Mississippi West was the frontier of an urban and industrial society. People, dissatisfied with their everyday lives, look westward and fantasize about simpler and better life.
I believe they represent the executive branch, however I am not sure.