A new computer method was developed to derive values of dip and vertical extent, as well as location, for the truncated face of a horizontal-plate model. The method is based on lateral offsets of the zero-crossover point of the second horizontal derivative of an upward-continued gravity profile. Application requires that the distance to the upper surface of the model be known. Numerical tests indicate useful results are obtained when both the length of the gravity profile, and the finite-strike length of a model are at least three times the maximum depth extent of the model. Gaussian noise with a standard deviation of 1 mGal can be tolerated given an anomaly amplitude of 70 mGal. An example from the Trans-Hudson Orogen of central Manitoba, Canada, indicates that the Kisseynew metasedimentary gneisses extend over a vertical distance of 16-18 km, and are separated from the Baldock batholith to the north by a near-vertical boundary.