Geometric studies in thrust belts have given rise to a number of kinematic models for the development of specific structural geometries, but the models have remained to a large extent untested for large scale examples because of a lack of sufficient incremental strain data and diagnostic microstructures. This project is designed to provide an adequate data set from well- exposed folds and thrusts in the northern Lost River Range in Idaho in order to constrain models for the development of those structures. The work involves construction of detailed 3-D structural geometries and cross-sections and the determination of strain histories using syntectonic fibers from samples collected from appropriate parts of these structures. Results are expected to allow a vigorous test of several hypotheses concerning how such folds and thrusts develop. The outcome will be utility in understanding the kinematics of deformation in other fold and thrust belts.