Excellent exposures in an area of multiple drape folds in the northwest corner of the Big Horn Mountains provide data for the construction of a three-dimensional model of the upper surface of the Mississippian Madison Formation. In the model, the vertical and horizontal scales are the same. Comparison of deformed and undeformed Madison surfaces indicate that displacements required by the deformation vary from place to place on the surface in both magnitude and direction. Calculations made from field measurements show that there is not enough fracturing or thinning in the Madison layer to account for the indicated displacements. Also, reasonable shortening on the basement faults underlying the forced folds cannot account for the calculated displacements in the sheet. Any solution to the mechanics of the drape-folding process must, therefore, meet the described constraints and still account for the indicated nonuniform displacements. Detachment of the sedimentary layers from the basement and intrastratal slip are two processes that meet the constraints and still account for the indicated nonuniform displacements.