Portland Basin (geology) explained

The Portland Basin is a roughly 770sqmi topographic and structural depression in the central Puget-Willamette Lowland.^[1] The Portland Basin isapproximately 40miles long and 20miles wide, with its long axis oriented northwest.^[2] Studies indicate that as much as 1800feet of late Miocene and younger sediments have accumulated in the deepest part of the basin near Vancouver. Most of the basin-fill material was carried in from the east by the Columbia River.^[3]

References

1. Beeson, M.H., Tolan, T.L., and Anderson, J.L., 1989, The Columbia River Basalt Group inWestern Oregon; Geologic Structures and other Factors that Controlled Flow EmplacementPatterns, in Reidel, ap. and Hooper, P.R., eds., Volcanism and tectonism in the ColumbiaRiver flood-basalt province, Geologic Society of America Special Paper 239, p223-246
2. Evarts, Russell C., 2004, Geologic Map of the boy Quadrangle, Clark and Cowlitz Counties, Washington, U.S. Geological Survey
3. 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