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Relief map showing the varying age of bedrock underlying North America. This cartographic tapestry is woven from a geologic map and a shaded relief image. This combination reveals the geologic history of North America through the interrelation of rock type, topography and time. Regional surface processes as well as continent-scale tectonic events are exposed in the three dimensions of space and the fourth dimension, geologic time. Image credit: USGS, GSC & MCRM |
