Start a campaign and hit start, then go to cheats:

BXXAX - Arizona Territory
BXXAY - Oklahoma Grasslands
BXXYB - New Mexico
BXXYA - Great Basin
BXXYX - Northern California
BXXYY - Southern California
BXXBB - Great Plains
BXXBA - Great Lakes
BXXBX - Dakotas
BXXBY - Central Heartland
BXXAA - Northern Texas
BXXAB - Southern Texas
BXXXA - Arcadia Plains
BXXXB - Northern Cascades
BXXXX - Southeastern Cascades
BXXXY - Central Cascades
BXYYA - Northern New England
BXYYB - Eastern Shenandoah
BXYYX - Ohio Valley
BXYYY - New York
BXYXA - Carolinas
BXYXB - Florida
BXYXX - Mississippi Delta
BXYXY - Cumberlands