Geological structures are three dimensional, yet are typically represented by, and - terpreted from, outcrop maps and structure contour maps, both of which are curved two-dimensional surfaces. Maps plus serial sections, called 21/2-D, provide a closer approach to three dimensionality. Computer technology now makes it possible for geological interpretations to be developed from the beginning in a fully three dim- sional environment. Fully 3-D geological models allow significantly better interpre- tions and interpretations that are much easier to share with other geologists and with the general...