Glacial Erratic Rock - Willamette Valley

Story by Lorita OLeary

Louise and grandson Ryan head up the trail to the site

Back during the last Ice Age (12,000 to 18,000 years ago) the Missoula Floods, originating in southwest Montana, deposited vast amounts of earthly debris over portions of Idaho, Washington and Oregon - eventually spilling into the Pacific Ocean.  Because of these floods, the Willamette Valley in Oregon became one of the most fertile regions in the state.  Vineyards sprung up - some 40,000 acres of grapes - which now produce some of the finest wines in the French Burgundy style.

At the top

When the 3,000 square mile prehistoric Glacial Lake Missoula flooded, the waters coursed through the Columbia River Gorge at 60-miles-per-hour carrying huge boulders with it.  Eventually the cataclysmic waters receded and what remained were “glacial erratics” stranded where they had come to rest. 

One such 90-ton boulder stands atop a hillside in McMinnville, Oregon surrounded by rich farmland and vineyards below. You can hike the 1/4 mile paved path year-round up to the site and see the largest glacial erratic found in the Willamette Valley. In fact, the only other place rocks like this have been found are in Canada. 

Soaking up the sun, taking in the view

My mother was raised on this hilltop in Yamhill County, her family moved there in the early 40s when she was 12, and she used to hike to the Rock throughout her childhood. It hadn’t been “discovered” yet and she knew it only as a cool rock and a good place to hang out (my slang, not hers). I also loved the rock as a child and remember finding it one day when I was at grandpa and grandma’s farm. It was a warm day and I climbed up on it’s sunny surface to daydream. I remember the rock seemed out of place here (being the only thing like it in the area) and I thought it was a special find, but I imagined it coming from outer space - like a meteor.

Over the years I traveled and moved to other states but was surprised to discover recently that the rock is somewhat famous and an Oregon State Park called Erratic Rock State Natural Site. Now anyone can climb to the top of the 250 foot hill to enjoy the scenery, the sun-soaked surface of this glacial erratic, and daydream.

After parking along Oldsville Road, there's an interpretive sign which allows visitors to learn about the rock. Once on top of the hill, there's a picnic table in case anyone brings a lunch.  On a warm day its nice to sit or lie on the rock and soak up the warmth. You will also be rewarded with spectacular vistas -vineyards, orchards, farms and the Oregon coast range.

Enjoy the behemoth, which is composed of metamorphic rock called argillite,  but leave it there because it seems to be shrinking. The reason: geologists estimate visitors have removed more than 70 tons of the rock over the years.

Park along Oldsville Road off of Highway 18 to reach this park. From Oldsville Road, you'll need to walk up the quarter-mile paved path to the rock itself. The trail becomes steep briefly as you near the rock. There is no fee to use this park.