[1][2] Robin Burnham (1994) specifies that these formations have not been defined and extended to Puget Group outcrops to the south within the Green River gorge and all of the Tukwila formation rocks are missing.
The Puget Group has been mapped across a total of six western Washington geographic quadrangles.
[1] The total deposition time has been estimated to be as short as approximately 7.7 million years, from around 45 to 36 million years ago based on isotopic data reported in 1993 or as long as 51 to 34 million years ago based on the paleofloristic data of Wolfe (1968, 1977)[1] The Western North American floras of the Eocene were divided into four floral "stages" by Jack Wolfe (1968) based on work with the Puget Group plant fossils.
[3] The beginning of the Kummerian was refined by Gregory Retallack et al (2004) as 40 mya, with a refined end at the Eocene-Oligocene boundary where the younger Angoonian floral stage starts.
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