The Meshik and Aleutian arcs of the Alaska Peninsula are magmatic arcs of predominantly calc-alkaline affinity. The Meshik arc, primarily of Eocene and Oligocene age, is in part stratigraphically equivalent to "early series" rocks of the Aleutian Islands. Its northeasternmost outcrops lie south of Mother Goose Lake, but rocks of the arc occur in the subsurface as far north as Becharof Lake. The Aleutian arc is of middle Miocene to Holocene age; it extends from Hayes Volcano in the southern Alaska Range to Buldir Island in the Aleutians. On the Alaska Peninsula, the dominant major volcanic-rock types in both arcs range from leuco basalt to dacite. Plutonic rocks of the Aleutian arc crop out in many places on the peninsula, including the Devils and Agripina Bay batholiths. ock types of the plutons are commonly quartz diorite, granodiorite, and lesser tonalite. Plutonic rocks of the Meshik arc are less common, though compositionally similar to Aleutian-arc plutonic rocks.

Both the Aleutian and Meshik arcs exhibit a shift in the locus of magmatism over time. Available data document a shift in the magmatic locus of the Aleutian arc about 50 km northwestward from the Pacific Coast in the middle Miocene to its present position. Less definitive evidence suggests that the Meshik arc shifted a similar distance to the southeast during Eocene and Oligocene time. Although segmentation of the Aleutian arc is well described, less evidence exists to suggest similar segmentation of the Meshik arc.

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