Rare rock discovered at Lake Oswego construction site

LAKE OSWEGO, Ore. — It was a normal day on the job for Jacob Parker.

He was on a construction crew working to build the new Lakeridge Middle School. But one of the rocks they excavated caught his eye.

“I had no clue what it was. I used a rock identifier app to try and identify it,” he said.

The app told him the rock might be radioactive, so he called in local geologist Scott Burns from Portland State University.

Burns told him it wasn’t dangerous but it was something extraordinary.

“Basically, this is just a very, very rare rock,” Burns said.

How rare? It’s from east of the Cascades, carried here by the Missoula Floods at least 15,000 years ago. Only one other rock like it has ever been found in our area.

“The thing is this is only the second one. We don’t know where the other one is. It was recorded in somebody’s notebook many, many -- a hundred years ago, but we don’t know where it is,” Burns said.


Scott Burns, a geologist at Portland State University, holds a piece of rhyolite. It came from a 2,000-pound piece of it that was found at a construction site for the new Lakeridge Middle School in Lake Oswego. It was carried here from east of the Cascades by the Missoula Floods at least 15,000 years ago.

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The rock is known as rhyolite and is created by layers of cooling lava, usually from close to the earth’s surface.

Students got pieces of it to take home with them.

The 2,000-pound rock is headed to the Tualatin Heritage Center to join an Ice Age flood exhibit.