Photoclinometric data for Lunae Planum wrinkle ridges indicate average relief of ~130 m and distinct elevation discontinuities across the ridge of 55 m. Modelling ridges as the result of thrust faulting and associated upper-plate folding indicates shortening across individual ridges of ~131 m (90% faulting). Total shortening at 20 ¿N across Lunae Planum is ~1840 m corresponding to a regional compressive strain of 0.29%. Strain appears uniform across Lunae Planum, although it is accommodated by larger and fewer structures in the west than in the east. ¿American Geophysical Union 1991