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This is
a geologic map showing the area of John Day. Formations are layers of rock
that are identifiable across large areas and formed near the same time. The
list of formations is always from the youngest down to the oldest. Miocene is
a range of time about 11 to 25 mya. Eocene is older about 40 to 50 mya range.
Mesozoic and Paleozoic are older longer time periods.
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