In the photo above we have the evidence of volcanic activity, earth upheaval, stream action, and erosion all in one place. The lighter rock was once magma buried deep within the earth. It pushed its way into the surrounding rock - the darker gneiss (pronounced nice) - where it solidified and crystallized into the granite we see today. Upheavals deep within the earth's crust forced the gneiss and granite to the surface, where a far wetter climate than what's present today cut the rock into a valley with a stream that carried sediment away. All of this occurring over millions of years, today showing us the contact zone where molten rock once met solid stone.
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