New 40K-40Ar and fission-track ages from volcanic ash partings in coal beds of the Eocene Puget Group of western Washington indicate a time span of about 41.2 ± 1.8 to 45.0 ± 2.1 (2σ) m.y. for the 1,890-m section of sediments exposed in the Green River area. These age data do not entirely support the previous early Eocene through early Oligocene paleobotanical age estimates for this section and for the four paleobotanical stages defined within it. Radiometric dating of floras assigned to the same stages outside the type section appears to be partially inconsistent with radiometric ages from the type section.

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