Natural History of Opal Creek
Standing in Jawbone Flats 30 million years ago, you would have been surrounded by huge conical volcanic peaks and huge mounded shield volcanoes studded with cinder cones, all covered in verdant tropical to subtropical rainforest. The scene would be reminiscent of the volcanic highlands of Costa Rica today. These peaks were part of the West Cascades mountain chain, a chain that predates the Cascades we are familiar with. These peaks went through vast cycles of eruption and erosion from 37 million years ago up until 7.4 million years ago, when the center of volcanic activity shifted east to its present location. Over millions of years following the volcanic shift, the West Cascades were worn away by the erosive powers of water and flowing glacial ice at higher elevations. The rounded, heavily forested ridges that surround you today are the remnants of these once great stratovolcanoes.
The rise and fall of the West Cascades and the development of the High Cascades set the topographic base upon which an ever changing succession of plant communities flourished. During the Oligocene Epoch, which lasted from 36 to 25 million years ago, the forests of this area were of a tropical and subtropical nature and species such as palm, avocado, and lancewood abounded. During the Miocene Epoch, which lasted from 25 to 13 million years ago, the forests were warm and temperate with ginkgo, dawn redwoods, hickories, redbuds, and sycamores. These forests resembled a mixture of those found in East Asia and the Southeast U.S. today. In the Pliocene Epoch, 13 to 2 million years ago, the forests of this area came to resemble those of today, but the climate was wetter and slightly warmer. This allowed species like persimmon and sweet gum to grow.
Starting about 2 million years ago the Northern hemisphere headed into an ice age known as the Pleistocene. The Pleistocene, as with all ice ages, did not mean a solid freeze. For the duration, the climate fluctuated on time scales of thousands and even hundreds of years. Colder, wetter periods meant the advance of glaciers, and warmer, drier periods the retreat. In the West Cascades, with the lower elevation, glaciers tended to only carve the upper ends of valleys.
Opal Creek was formed in this way, as a glacier at the head of the Opal Creek valley scooped out its basin that filled with water after the glacier's retreat. This event took place about 15,000 years ago during the last glacial maximum. At this time the vegetation of this area most closely resembled plant communities today found in alpine and tundra areas.
After the maximum the climate generally trended toward warmer and drier, and the glaciers retreated. Starting at about 9,000 years ago the climate entered a period that was warmer and drier than today. The forests during this period were comprised of more drought and fire tolerant species. These species moved in from the southern reaches of the Pacific slope. Starting about 6,000 years ago the climate started to shift and once again became cooler and wetter. It was at this time that many of the mega-conifers that make up today's forests slowly migrated into the Pacific Northwest from the North, following the cooling climate. The coniferous temperate rainforests found on the Pacific slope today are unparalleled throughout the world and, according to all present fossil evidence, unparalleled throughout the history of this planet. These forests have no equal in the heights, longevities, and pure living mass attained by numerous tree species. Over the eons these trees and millions of associated organisms have interwoven to form a system that is incredibly complex and diverse. These forests are truly one of the greatest ever expressions of life, and now the fate of what remains of this truly unique system is in the hands of our species.
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