In the quiet Portland suburb of Tualatin, glacial erratics from the Missoula Floods share museum space with mastodon tusks and teeth -- artifacts from two very different chapters of the ice age that intersected in this valley. The Tualatin...
In the quiet Portland suburb of Tualatin, glacial erratics from the Missoula Floods share museum space with mastodon tusks and teeth -- artifacts from two very different chapters of the ice age that intersected in this valley. The Tualatin Heritage Center houses boulders that floated into the Willamette Valley on icebergs during the floods, alongside fossils of the giant mammals that roamed the valley between flood events. The Tualatin area was repeatedly inundated when floodwaters backed up from the Columbia Gorge and filled the Willamette Valley to depths of 300 to 400 feet, creating temporary Lake Allison. When the waters receded, they left behind fine sediments, scattered erratics, and a landscape that attracted Pleistocene megafauna. The Tualatin Ice Age Walking Trail, a self-guided tour connected to the Heritage Center, leads visitors to sites where erratics, mastodon remains, and flood deposits have been found throughout the community. Water-themed artwork along the trail pays homage to the floods that shaped this valley. For a suburban community, Tualatin holds a remarkable concentration of ice age evidence just beneath its lawns and sidewalks.
The Tualatin Heritage Center is operated by the Tualatin Historical Society at 8700 SW Sweek Drive in Tualatin, Oregon. Open limited public hours (typically several days per week and for special events); admission is free or donation-based. The center houses Ice Age fossils, Columbian mammoth and mastodon tusks, smaller bones, and displays granite-erratic boulders with interpretive plaques on the grounds.
Tualatin sat squarely at a flow path junction of the Missoula floods, with backflood from the lower Columbia entering the Tualatin Valley through the Lake Oswego gap and exiting back through the same constriction, more than 40 times during the flood interval (roughly 18.2 ka through 14.0 ka per Balbas et al. 2017 and follow-on cosmogenic work). Peak inundation in the valley reached approximately 400 feet above today's sea level. Each flood deposited a layer of Willamette Silt and rafted erratic boulders embedded in iceberg ice that had drifted in from the disintegrating Lake Missoula dam; the Heritage Center's erratics are local examples. The on-site fossils (mammoth, mastodon) come from the Tualatin floodplain and represent megafauna that lived in the valley during and between flood episodes.
The Tualatin Ice Age Foundation continues fundraising and planning for the Willamette Valley Ice Age Interpretive Center. The Heritage Center recently received a new erratic for display (Tualatin Life coverage). Pacific Mastodon taxonomic revisions (Dooley et al. 2019 and follow-on work, including Boehm at the University of Oregon) have implications for fossil identifications in the area, including the famous library mastodon (see next entry).
The Lower Columbia Chapter of IAFI covers the Willamette Valley and partners with the Tualatin Historical Society, City of Tualatin, and Tualatin Ice Age Foundation. The 2021 visitor-center dedication at the Tualatin Public Library involved Lower Columbia Chapter participation.
Year-round but with limited hours, check the historical society's schedule before visiting. Pair with the Tualatin Public Library, the Ibach Park play features, and the Tualatin River Greenway timeline panels for a half-day walk through the city's Ice Age branding.
Flood-extent overlay shows the maximum reach of the Missoula Floods.
The site in its place along the flood path, with the maximum flood extent drawn over the modern map.
View on the interactive map Searchable sites · 360° trails · flood reconstruction