thunder egg

Asked January 23, 2017, 1:58 PM EST

My folks have what we think is a large thunder egg that was brought here with the Montana flood hundreds of years ago.We found it at the back of thier30 acres back in the early 60s and it had a 1" hole drilled in it by one of the local farmers back in the 40s.Its perfectly round and stands about 3' tall .Its the only rock we have found on the place,and we are curiuos as what to do with it.

Washington County Oregon geology

1 Response

Hi! From your description you have a glacial erratic. Wonderful! It rafted in on one of the many Missoula Floods (Ice Age Floods). The Willamette valley is littered with boulders that came in on chunks of ice, rolled in the flood waters and were parked high and dry as the waters receded.

Since you live near Portland, there are a number of geologists who can help you identify the type of rock. A lot of the glacial erratics are granite, quartzite and other types of rocks, different from our common black basalt.

You can take a picture of the rock and send it to either Portland State University or the Department of Oregon Geology and Mineral Industry, asking for a geologist to identify it. You can also attach a photo to this website.

Appreciate your piece of Missoula Flood history! It came a fair distance to the Oregon Country.