The Portland Basin is a roughly topographic and structural depression in the central Puget- Willamette Lowland. The Portland Basin is approximately long and wide, with its long axis oriented northwest. Studies indicate that as much as {{convert, 1800, ft, m of late

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

and younger sediments have accumulated in the deepest part of the basin near

Vancouver Vancouver ( ) is a major city in western Canada, located in the Lower Mainland region of British Columbia. As the List of cities in British Columbia, most populous city in the province, the 2021 Canadian census recorded 662,248 people in the ...

. Most of the basin-fill material was carried in from the east by the Columbia River.Liberty, L.M., Hemphill-Haley, M.A., and Madin, I.P., 2003, The Portland Hills Fault –uncovering a hidden fault in Portland, Oregon using high-resolution geophysical methods, Tectonphysics, v.368. p. 89-103

References

Structural basins of the United States Geology of Oregon Geology of Washington (state)