A Look at Sisters Country Geologic History
by Janet L. Brown

Everything was peaceful in “Sister’s Country” until about 250 million years ago. The pleisiosaurs were jumping in the ocean; the sun was shinning…..


Large-Headed Pleisiosaur: POLYPTYCHODON

The Large-Headed Pleisiosaur lived in Oregon Jurassic seas about 150 to 200 million years ago. It is the first Pleisiosaur skull discovered in the Pacific Northwest and was discovered in Central Oregon in 2004. The fossil is one line of evidence indicating that much of Oregon was covered by ocean in Jurassic times.



About 250 million years ago, the breakup of the supercontinent Pangea and the opening of Atlantic Ocean were initiated. Next

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