Rare 2-Ton Erratic is New Exhibit at Tualatin Heritage Center
A two-ton boulder of rhyolite igneous rock, not normally found in Oregon, was exposed during excavation work at the new Lakeridge Junior High School project in Lake Oswego. The boulder is believed to have been deposited in the Willamette Valley by the Missoula Floods around 15,000 years ago. The huge chunk of rhyolite is believed to have come from Montana or further north in Canada and floated to Oregon embedded in a glacial iceberg floating in one of the several massive Missoula Floods.
Scott Burns, a Portland State University Geology Professor and Tualatin Ice Age Foundation Board President, said the find is unique in his many years of research experience and will be a key display piece for the future visitor center the Foundation hopes to one day open in Tualatin. “We believe it’s an ice-rafted glacial erratic,” Burns said. “That is, it fell onto the glaciers up in British Columbia, Alberta, Canada or Montana and then was part of the dam that blew apart in the Missoula Floods and it floated down here and was then dropped.”
The Lake Oswego School District and the Foundation quickly produced an agreement that allowed the Foundation to take possession of the boulder and transport the specimen from Lake Oswego to the Heritage Center. In the next months interpretive information will be placed next to the stone.
Ross Baker, President of the Tualatin Historical Society which operates the Heritage Center said, “We’re a small facility and we pride ourselves on the exhibits we have both inside and out, The ice age items allow us to do both, because inside we have the mastodon tusk and other information, but outside is cool because the erratic rocks are there along with the heritage garden, and the overall blend is always improving. Every time the Ice Age fans get excited it’s always good for us.”