Geologic map of part of the Grand CanyonThe Inner Gorge is the area near the Colorado river underlain by Precambrian igneous and metamorphic rocks and overlying Proterozoic sedimentary rocks. In the map here, the Inner Gorge rocks are the Vishnu Schist (pink) and Trinity Gneiss (Orange). The contact between these two is nearly vertical as can be seen by the contact at "B". There, the contact does not conform to the topography in the least, but instead, cuts straight across it. The Cambrian Tapeats Sandstone, which overlies these rocks with profound unconformity at "A", is the teal colored unit. We can tell it is approximately horizontal because it follows the topography: note how it is everywhere equidistant from canyon bottoms and how the overlying contacts are everywhere parallel to it. On the right side of the map, you can see the Tapeats truncating the pink and orange-colored basement rocks.

For a view of the Inner Gorge, click here.

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