These are the sample data for creating surface with fault - a small
watershed with gully. The format is 
x y elevation label
Extract the faultline labeled as L,AA and L,BB using awk

B,BL,BOUNDARY LINE
S,ST,STATION
S,TB,TEMP. BENCHMARK
S,LOWER,60 D NAIL
S,UPSOUTH,UPPER SOUTH 60 D NAIL 
L,AA,TOP HIGHBANK OF GULLEY(FAULTLINE)
L,BB,TOP HIGHBANK OF GULLEY(FAULTLINE)
L,OGTRDX,OLD GEORGETOWN ROAD
S,UPNORTH,60D NAIL 
S,UPWEST,60D NAIL
S,ALPT1X
A
G
R