landslide product consisting of a very large block of undisturbed material that has been tilted backward toward the parent cliff during movement down a gentle slope. In northeastern Arizona such blocks are thought to have formed during more humid periods of the last glacial advance of the Pleistocene Epoch (1,600,000 to 10,000 years ago). Toreva blocks also occur, however, as a simple product of gravitational gliding in the Swiss Alps and in other ranges in humid regions.