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:: Home > The People > Biological Legacy: A timeline > Mesozoic

 

100
million years ago

100 Million Years Ago

During the Mesozoic Geologic Period, from 230 to 70 million years ago, the fossil record in Oregon was completed. A large, inland sea covered much of the state, and plants probably colonized near the water's edge. Those falling into the mud became over time the fossils we find today.

Flowering plants and grasses became common. This was the age of the spread of deciduous* trees, although such trees wouldn't colonize land in what is now Oregon until later. A warm and humid climate covered Oregon with little differentiation between western and eastern Oregon, because no mountain ranges had formed by this time.

* A deciduous tree loses its leaves at some point during the year. In today's Oregon, for example, our deciduous trees (e.g. maple, ash, cottonwood, aspen) are leafless over winter.

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