C

• [+] Colorado Plateau (1 C, 72 P)

D

• [+] Mojave Desert (8 C, 55 P)
• [+] Sonoran Desert (6 C, 27 P)

G

• [+] Grand Canyon (4 C, 76 P, 1 F)

G cont.

• [+] Great Basin (13 C, 107 P)

P

• [+] Pacific Northwest (8 C, 27 P)

R

• [+] Rio Grande (2 C, 16 P)
• [+] Rocky Mountains (4 C, 33 P)

S

• [+] Sierra Nevada (7 C, 189 P, 5 F)
• [+] Southwestern United States (11 C, 8 P)

Y

• [+] Yellowstone (6 C, 64 P, 1 F)

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

O cont.

• Osage Plains

P

• Prairie Pothole Region

S

• Southwestern United States