Two northwest-trending belts of eruptive centers, termed the Eastern Absaroka belt and the Western Absaroka belt, extend northwestward from the southeastern part of the Absaroka Range through the Gallatin Range. The belts were evidently zones of crustal weakness dating from Laramide or earlier time and lasting into the early Tertiary, when they served as conduits for volcanic and intrusive rocks of the Absaroka-Gallatin volcanic field. Igneous rocks of the Eastern Absaroka belt are more potassic than those of the Western Absaroka belt.

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