More than 10,000 years ago a slab of Tertiary limestone 15 km long slid off the northern flank of Kabir Kuh in the Zagros Mountains of southwestern Iran, producing a landslide that crossed two valleys and an intervening ridge and extended 20 km from its source. The slide must have been triggered by an earthquake, but the limestone slab probably had previously been undercut by the Saidmarreh River. Evidence is not adequate to postulate lubrication by a layer of compressed air; instead, pulverized marl and a sliding surface of gypsum bedrock may account for the distant travel. The surface of the slide is crisscrossed by ridges and troughs and by large grabens, mostly related to collapse over subsurface cavities produced by solution of gypsum bedrock after the slide occurred, both during outseepage of dammed lakes and, subsequently, after the lakes were drained by erosion of the outlets. The surface features resemble those formed on drift-mantled stagnant glaciers or by solution on limestone, that is, karst.