Recent discoveries in earth sciences are mostly related to technologies allowing graphical representations of volumes. We present a way to produce mathematically and geometrically correct three-dimensional (3-D) geologic maps consisting of the volume and shape of all geologic features of a given area. The method is innovative in that it only uses surface information based on the combination of a standard geologic map, a satellite image, and a digital elevation model. It is based on a modeling algorithm that only uses surfaces calculated from scattered data points and that intersects them following a series of geologically sound rules. The major advantage of using such technology is that it provides the user with a way to quantify geology. To illustrate how a 3-D geologic map can be computed, we explain the steps taken to build a dummy model with simple faulting and depositional sequencing. The case study chosen to illustrate the method is the Beirut watershed (Lebanon), an area with relatively simple geology. The 3-D visualization and cross sections help in the understanding of the geometrical relationship between the different geologic features, allowing a reexamination of the tectonic history of the area during the late Mesozoic.