C

• [+] Colorado Plateau (1)

D

• [+] Mojave Desert (7)
• [+] Sonoran Desert (7)

G

• [+] Grand Canyon (4)
• [+] Great Basin (13)

P

• [+] Pacific Northwest (10)

R

• [+] Rio Grande (2)

R cont.

• [+] Rocky Mountains (3)

S

• [+] Sierra Nevada (5)
• [+] Southwestern United States (11)

Y

• [+] Yellowstone (6)

C

• Cross Timbers

G

• Great Basin
• Great Plains

H

• High Plains (United States)

I

• Intermountain West

L

• Llano Estacado

M

• Mormon Corridor
• Mountain States

N

• Northwestern United States

O

• Ogallala Aquifer
• Osage Plains

P

• Prairie Pothole Region

S

• Southwestern United States