Introduction
Inverted topography is a classic type of landform in the American southwest with its young monogenetic volcanic fields and rapid arid-land erosion. Many volcanic deposits, whether they are lava flows or ash-flow-tuffs, flow down river valleys and topographic lows and even fill them. Because they are resistant to erosion, the volcanic rocks may erode away more slowly than the rocks that had made the sides of the former valleys. With time and this process of differential erosion, lava flows that once travelled down valleys later stand as mesas. This process reverses the elevation of volcanic features relative to other features; e.g., lava-filled valleys become mesas, and, in turn, former topographic high points become valleys.
Source: U.S. Department of the Interior, National Park Service
