Hillsboro Flood Evidence

Evidence of the Bretz (Missoula) Floods covers parts of 4 states. (Montana, Idaho, Wash., Oregon) This blog illustrates evidence of those floods in and around Hillsboro, Oregon.

Monday, June 27, 2005

Excavation for new Baseline Road bridges for Rock/Beaverton Creeks

At the end of the last ice age, about 12,000-18,000 years ago, there was a series of catastrophic floods that inundated the Columbia River basin and most of its tributaries.
The series of floods (probably lasting over 2,000 years) was first postulated by J. Harlen Bretz in the 1920s.

The above picture was taken along SW Baseline Road, looking west, east of Hillsboro, Oregon where it crosses Rock Creek and Beaverton Creek (Entrance to the Stonebriar sub-division). Several sand/silt layers (rhythm-ites) are evident. The flooding Columbia River pushed the Wilamette River, Tualatin River, as well as both Rock and Beaverton Creek backwards! The heavier sand layer was laid down first and then the silt layer as the water slowed and evetually drained down the Columbia.