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The Healy quadrangle Is underlain by a wide variety of sedimentary, volcanic, and plutonic rocks, ranging In age from Precambrlan and (or) early Paleozoic to Recent. There are fifty five map units on the geologic map. All the pre-Cenozolc rocks are Intensely deformed, mainly by overthrusting and folding, and most of them underwent at least one period of low-to medium-grade regional metamorphlsm. This deformation 1s the result of the middle Cretaceous collision and subsequent obductlon of the northward-moving Talkeetna superterrane with and onto the Yukon-Tanana and Nixon Fork terranes of the ancient North American continent. Late Cenozoic deformation, the result of continued northward plate motions, has modified but not substantially altered the geology of the quadrangle.