I80 Westbound Rest Area, Grinnell

 The theme of the Grinnell Westbound rest area is the family farm.  The Grinnell Eastbound focuses on Grinnell University.

Tiffin I80 Rest Area West Bound

 The east bound I80 rest area is one of letters, where authors with local ties are highlighted.  The westbound Tiffin rest area focuses on education, including agricultural education.  There are also some letter blocks.

Council Bluffs, Pottawattamie County Rest Area, West Bound.

 This rest area is at mile marker 17 on the I80 in Iowa.  It appears to be an older and smaller rest area.  There is no theme that I could see. 

Herbert Hoover: West Branch, Iowa Rest Area.

 Herbert Hoover was from West Branch, Iowa.  This is a bit east of Iowa City.

A representation of local crops