From their origin in ArcInfo and the Alacarte package, each
coverage contains topological and bookkeeping attributes of
little or no scientific interest; only the attributes of
scientific significance are described in detail here.  The
other attributes are AREA, PERIMETER, LENGTH, FNODE#, TNODE#,
LPOLY#, RPOLY#, cover#, cover-ID, SEL, and SYMB.
The primary layer is the geology layer (gran-geo), which
consists of both polygon features and arc features that
describes map units (polygons), and depositional contacts,
faults (which may or may not be polygon bounding features) and
map boundaries.
Map units (polygons) are described in the polygon attribute
table (gran-geo.pat).  The identities of the map units are
recorded in the PTYPE field by map label (i.e. Ts). For a
description of the map units, consult the PostScript or PDF
explanation pamphlets in this report.
Geologic lines (arcs) are recorded as strings of vectors and
are described in the arc attribute table (gran-geo.aat). They
define the boundaries of the map units, the faults, and the map
boundaries. These distinctions, including the geologic
identities of the unit boundaries, are recorded in the LTYPE
field. Attributes for geologic lines generally follow a scheme
of the type of geologic line (i.e. fault), followed by a
locational and/or scientific modifier (i.e. approx. located or
queried).
The geologic structure layer (gran-str) consists of point
features that describe geologic structures such as strike and
dip of beds.  Point features, typically structural
measurements, are described in the point attribute table (gran-
str.pat) and are used to represent locations of structural
measurements such as strike and dip, and foliation.  The type
of structural measurement of points is attributed in the PTTYPE
field, and the measurements taken at that location are
attributed in the STRIKE and DIP fields.
Features representing location of samples (gran-smp) discussed
in the original report, are described in the point attribute
table (gran-smp.pat).  Attributes of features in this dataset
are recorded in the PTTYPE field, and the sample number from
the map is recorded in the SAMPNO field.

http://pubs.usgs.gov/of/2002/0273/pdf/of02-273_1a.pdf

Arcs of geologic significance

Geologic units

Samples

Structural measurment