The Troutdale Formation was named by Hodge (1938) for thick beds of gravels and sands exposed as cliffs along the Sandy River near the town of Troutdale, Oregon.
Evidence of scouring and broken off chunks of Troutdale Formation bedrock below the [Round Lake] dam testify to the erosive power of water over time.
A stratigraphic-geochemical study of the Troutdale Formation and Sandy River Mudstone in the Portland basin and lower Columbia River Gorge, figure 3
A stratigraphic-geochemical study of the Troutdale Formation and Sandy River Mudstone in the Portland basin and lower Columbia River Gorge (pdx.edu)
Round Lake Loop Interpretive Trail Guide (PDF) (clark.wa.gov) This guide describes various water related features around Round Lake which corre spond to numbered trail-side posts.
