For this month, my book group chose a novel by Tracy Chevalier called Remarkable Creatures, about 2 British women who made important fossil finds in the cliffs outside their seaside village in the 1800s. I am enjoying it so far–and it got me thinking about the fossils I had found right here at home a while back.
New homes were being built in the woods behind us, and a deep trench was dug for the water and sewer lines. Six to eight feet down, layers of orange, pale green, and yellow ochre clay rocks were visible. The heavy machinery spewed these rocks out of the trench–and they were filled with fossils. It was fascinating. The rocks were easy to split into layers, and in the layers were impressions of clams, tube worms, and snails. It seems that our woodsy, hilly home had once been under the sea . . .
I did some research. Way back in the Eocene Era, from 34 to 56 million years ago, the Southern Willamette Valley was indeed under water. It was part of a deep bay with the inlet in the north, (Portland would have been a deep-sea port) and it lasted for 25 million years. The layers of sediment that formed on the bottom are over a mile thick.
The climate was warm then. Volcanos were actively erupting and the Western Cascades were formed–the eroded remnants of which form the Coburg Hills today, as well as the cliffs above the McKenzie Bridge and Opal Creek areas. These areas formed the shores of the vast bay. As time went on, the seabed rose, and the bay drained.
The site of my home became part of a vast, quiet, swampy, grassy valley. It was roamed by elephants, giant bison, and ground sloths. Rivers carved it, ice ages shaped it. As the climate warmed once more, flooding from Ice Age melting made the Willamette Valley into a lake 100 miles long, 60 miles wide, and 300 feet deep. This lake left left about 15 feet of layered, sticky sediment.
I learned all of this information from a beautifully illustrated, fascinating book called In Search of Ancient Oregon, by Ellen Morris Bishop. I checked it out of the library and highly recommend it.
I wonder which era my fossils are from–that truly ancient seabed of the Eocene era, or the more recent Pleistocene lake. I suspect the latter is more likely: that my hilly neighborhood was along the edge of the huge lake, and that my fossils were the creatures that lived in the muddy, marshy shores: freshwater clams and snails. It boggles my mind to imagine the span of time, and to try to visualize all the changes my little plot of yard has undergone throughout the ages.