B & R    Basin and Range
BM       Battle Mountain High
CB       Columbia Basin
CP       Colorado Plateau
CTAZ     Cordilleran Thermal Anomaly Zone
CVA      Cascade Volcanic Arc
EL       Eureka low
GP       Great Plains
MR       Middle Rocky Mountains
NR       Northern Rocky Mountains
PR       Pennisular Ranges
RG       Rio Grande rift subprovince
SA       San Andreas fault
SB       Salinian block
SN       Sierra Nevada
SR       Southern Rocky Mountains
SRP      Snake River Plain
ST       Salton Trough
TG       The Geysers/Clearlake area
WB       Wyoming Basin
WV/CR    Willamette Valley/Coast Range
Y        Yellowstone