Landscapes are the product of erosion on areas of varying rock type and tectonic features. The tectonic features are the result of processes that include
- igneous rock intrusions, especially as manifested in volcanoes
- folding
- faulting.
The effects of erosion reflect the main erosion agents:
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Maps such as this computer generated shaded relief map of the US (prepared by the US Geological Survey) show more relief in areas of recent modification of the land by tectonic forces, such as the western US. Areas that have been tectonically quiet for long period such as the central US show little topographic relief. Areas of older tectonic activity as in the eastern US show relief but it is subdued relative to the west. This is because erosion has acted longer on those rocks than on the features in the west. |
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On the east and Gulf coasts the land is flat where new materials are accumulating, building out into the ocean and enlarging the continent. These are the coastal plains. On the west coast where the edge of the continent is steep sedimentary materials have not accumulated in enough thickness to reach sea level.
If you want to learn more about the topographic features shown on this map and their underlying geology check out A Tapestry of Time and Terrain: The Union of Two Maps - Geology and Topography where the USGS shows the merged topography and underlying geological units.