Claim: Two hundred million years ago, a large mass of igneous rock was created as two land plates overlapped; the rock is visible as granite domes at Sierra Nevada Batholith which are thought to be the roots of subduction zone volcanoes.
Evidence: Around 200 million years ago, the ancient oceanic Farallon Plate began to subduct beneath the North American Plate. As the Farallon moved eastward, it was overridden by the North American, and the moisture within it was figuratively baked out of the rock before the crust melted into magma. As it began to cool, a large mass of igneous rock was created and is now visible as the granite domes of the Sierra Nevada Batholith. Batholiths are large masses of igneous rock that form deep below the surface, and they are thought to be the "roots" of subduction-zone volcanoes.