Bishop, Ellen Morris. In Search of Ancient Oregon: A Geological and Natural History. Portland: Timber Press, 2003. (Reviewed by Kate Koehler)
In Search of Ancient Oregon: A Geological and Natural History, written by Oregon geologist Ellen Morris Bishop, is a “book for those interested in Oregon's present and past landscapes, plants, animals, and climates” (book jacket). This book explains Oregon's geological history in a chronological order, beginning with Oregon's oldest rocks, 400 million years old, and continuing through the Paleozoic, Paleocene, Eocene, and Holocene eras. It covers topics such as the subduction zone of the Blue Mountains, the burial of the Wallowa volcanoes, the granites in the Klamath Mountains, the source of the Columbia River basalt, the formation of the Cascades, the history of Mount Mazama, and the beginning of human history in this area, among other things.
This book also contains information specific to the forming of the Willamette River valley. It explains that in the Eocene era the coast reached the edge of the Willamette Valley, and that during the Oligocene era the valley filled with eruption from the Colestin formation. It also explains the flooding of Lake Missoula, which “transformed the Willamette Valley into a lake 100 miles long, 60 miles wide, and 300 feet deep” (pg. 227). This flooding brought 15 feet of murky sediment to all parts of the valley, which is why the valley is so fertile. “Today, more that 300 ft of sediment from the Missoula and Bonneville floods lie in the floor of the Willamette Valley” (pg. 229).
The book concludes with an epilogue explaining how humans have changed the landscape of Oregon. It also theorizes about the future; as humans continue to destroy the natural environment, fewer species will exist. Biologist E.O. Wilson predicts that “20% of all species present at the beginning of the Holocene era will be extinct by 2050” (pg. 255). The book ends with a reminder that although humans can and do change the natural environment, natural geological change will always continue.
I really enjoyed looking at this source. It is presented in an easy-to-read format, and includes innumerable full color photos of the Oregon landscape. Although it does not focus just on the Willamette Valley, it contains information about the formation of the valley and river, and offers a larger geological context for the valley. It does not, however, mention anything about the Mount Mazama ash contributing to the formation of the valley.
The book is not good for looking at recent changes of the Willamette Valley, because it is written on a geological time scale. It also focuses mainly of geology, so is a good source for that specific topic. The extensive bibliography in the back includes other resources on the natural history of Oregon. I found this book very interesting and easy to understand.
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