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Erratic Rock

From Oregon Hikers Field Guide

View from the rock in winter, Erratic Rock State Natural Site (bobcat)


The Bellevue Erratic is a 90-ton argillite metamorphic rock, a mere remnant of the 160 tons that settlers discovered: generations of decidedly un-classy visitors have chipped at it to carry off souvenirs and, even today, graffiti besmirches the surface.

The rock is the Willamette Valley's largest relic of a time when the entire expanse that is now vineyards and fields was drowned periodically by catastrophic floods. Towards the end of the last Ice Age, a cycle of massive floods, known as the Missoula or Bretz Floods (after the geologist J. Harlen Bretz) hurtled at 60 mph down the course of the Columbia River all the way to the Pacific Ocean. These floods, perhaps up to 100 of them between 15,000 - 18,000 years ago, came as huge ice dams gave way at the end of the Ice Age and massive amounts of meltwater from the continental ice sheet were released. The floods scoured away topsoil, carved valleys, and deposited sediments all along their course, but also transported large icebergs, some of them rafting massive boulders. One such iceberg raft, perhaps one of the largest, came to rest on a small prominence in what is now Yamhill County as the floods filled the Willamette Valley. The iceberg had a passenger, the so-called Bellevue Erratic, a massive boulder from the Canadian Rockies which presides over expansive views of Oregon's wine country from the Erratic Rock State Natural Site.

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