Go Upper Midwest!
From the looks of it, the proving ground, for class E anyway, appears to be Minnesota, Iowa, the Dakotas, and Wisconsin.
Gotta love it!
Class Code Airport
B CVG Cincinnati/Northern Kentucky International Airport
B MIA Miami International Airport
B PHX Phoenix Sky Harbor International Airport
C ANC Anchorage International Airport
C GRB Green Bay- Austin Straubel Int'l Airport
C LNK Lincoln Airport
C RNO Reno- Tahoe International Airport
C SJC San Jose International Airport
D LHD Lake Hood Seaplane Base
D MRI Merrill Field
E ABR Aberdeen Regional Airport
E AMW Ames Municipal Airport
E ATY Watertown Regional Airport
E AXN Alexandria Municipal Airport
E BJI Bemìdji Regional Airport
E BKX Brookings Regional Airport
E BRD Brainerd Lakes Regional Airport
E CIU Chippewa County International Airport
E CMX Houghton County Memorial Airport
E DIK Dickinson Airport
E DVL Devils Lake Regional Airport
E EAR Kearney Regional Airport
E ELO Ely Municipal Airport
E ESC Delta County Airport
E FFM Fergus Falls Municipal Airport
E FOD Fort Dodge Regional Airport
E FRM Fairmont Municipal Airport
E HIB Range Regional Airport
E HON Huron Regional Airport
E HSI Hastings Municipal Airport
E IKV Ankeny Regional Airport
E IMT Ford Airport
E INL Falls International Airport
E IWD Gogebic- Iron County Airport
E JMS Jamestown Regional Airport
E MCW Mason City Municipal Airport
E MHE Mitchell Municipal Airport
E MKT Mankato Regional Airport
E OFK Norfolk Regional Airport
E OLU Columbus Airport
E OSC Wurtsmith Air Force Base
E OTG Worthington Municipal Airport
E PIR Pierre Regional Airport
E PLN Pellston Regional Airport
E RHI Rhinelander- Oneida County Airport
E RWF Redwood Falls Municipal
E SLB Storm Lake Airport
E SPW Spencer Municipal Airport
E TVF Thief River Falls Regional Airport
E YKN Chan Gurney Airport