Troutdale Formation

field trip

Columbia Gorge Field Trip: Troutdale Formation and Boring Basalt (cwmh2o.com) The CwM team could not resist the early summer-like weather in the Pacific Northwest and took a “Geology-Friday” field trip into the Columbia River Gorge. Their trip took them east from Portland to the Sandy River, along the Historic Columbia River Highway through Corbett, with stops at the Latourell and Bridal Veil Falls, and back west along the banks of the Columbia River. The goal was to find outcrops of the Troutdale Formation, parts of which make up an important groundwater source in the Portland metro area and part of the City of Portland’s Columbia River Wellfield.

geological formation of

namesake of

Troutdale, Oregon

naming

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.

potholes

Fast swirling water carries loose rocks which grind holes in the softer Troutdale Formation

random

The star’s Arabic name derives from a word meaning “the groin” of the celestial Bear that plods silently around the north celestial pole (the name mistakenly drawn from Merak, in the Dipper’s bowl).

Round Lake Dam

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.

stratigraphic column

A stratigraphic-geochemical study of the Troutdale Formation and Sandy River Mudstone in the Portland basin and lower Columbia River Gorge, figure 3

stratigraphic-geochemical study

A stratigraphic-geochemical study of the Troutdale Formation and Sandy River Mudstone in the Portland basin and lower Columbia River Gorge (pdx.edu)

tags

trail guide

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.