The database consists of eight coverages (excluding the coverages mentioned in the Supplemental_Information element)
>The individual attributes for each coverage are described as follows (*=DVRFS):
>--------POLYGONS-<*_GEO>
>UNIT: see map text for explanation of lithologic unit symbols
>&=Pennsylvanian
>@=Triassic
>_=Cambrian
>UNIT_CODE:
>1=surficial Quaternary unit
>2=igneous Quaternary unit
>3=sedimentary Tertiary unit
>4=volcanic Tertiary unit
>5=intrusive Tertiary unit
>6=sedimentary Mesozoic unit
>7=igneous Mesozoic unit
>8=sedimentary Paleozoic unit
>9=igneous Paleozoic unit
>10=Precambrian unit
>TECT_CODE:
>0=no tectonic significance assigned
>1=Mesozoic intrusive rocks
>2=Tertiary intrusive rocks
>3=Proterozoic basement rocks (base of ground-water model)
>SYMBOL: value from CTR269 shadeset for coloring polygons
>--------ARCS-<*_GEO, *_FLT, *_GPFLT, *_CALD, *_LIN, *_TLINE, *_WLANE>
>TECT_INDEX (*_FLT only):
>0=not regionally significant structure
>1=regionally significant structure
>LABEL (*_CALD, *_LIN, *_TLINE, and *_WLANE only):
>character attribute describing structure
>LINE_CODE, DESCRIPTION (*_GEO, *_FLT, *_GPFLT and *_CALD only):
>1, "contact-certain"
>2, "contact-inferred"
>10, "contact-faulted" +
>20, "fault-certain"
>21, "fault-inferred"
>22, "fault-concealed"
>23, "fault-queried"
>30, "thrust fault-certain"
>31, "thrust fault-inferred"
>32, "thrust fault-concealed"
>40, "low-angle normal fault-certain"
>41, "low-angle normal fault-inferred"
>42, "low-angle normal fault-concealed"
>60, "caldera boundary-certain"
>62, "caldera boundary-concealed"
>90, "geophysically inferred structure-well constrained"
>91, "geophysically inferred structure-poorly constrained"
>99, "map area boundary"
>+ code=10 is used for lines which represent both fault lines and unit contacts in DVRFS_GEO.  It is a cartographic designation for lines repeated in both the geology and fault coverages so that they will not be drawn twice in plotting and is not used uniformly due to inconsistent attribution of source data.
>SYMBOL: value from GEOSCAMP1 lineset for drawing lines
>--------ARC-<*_SYM>
>SYMBOL:
>1= bar and ball symbol
>2= bar and ball symbol (geophysically inferred structure)
>3= right-lateral offset arrows
>4= right-lateral offset arrows (geophysically inferred structure)
>5= left-lateral offset arrows
>6= left-lateral offset arrows (geophysically inferred structure)
>--------POINT-<*_SYM>
>SYMBOL:
>1= bar and ball symbol
>2= bar and ball symbol (geophysically inferred structure)
>3= right-lateral offset arrows
>4= right-lateral offset arrows (geophysically inferred structure)
>5= left-lateral offset arrows
>6= left-lateral offset arrows (geophysically inferred structure)
>ANGLE: angle to plot offset symbol

http://pubs.usgs.gov/mf/2002/mf-2381/mf-2381-a/mf-2381-a_p.pdf