Portland (/?p??rtl?nd/) is the largest city in the U.S. state of Oregon and the seat of Multnomah County. It is located in the Willamette Valley region of the Pacific Northwest, at the confluence of the Willamette and Columbia rivers.
During the prehistoric period, the land that would become Portland was flooded after the collapse of glacial dams from Lake Missoula, located in what would later become Montana. These massive floods occurred during the last ice age and filled theWillamette Valley with 300 to 400 feet (91 to 122 m) of water. Before American pioneers began arriving in the 1800s, the land that eventually became Portland and surroundingMultnomah County was inhabited for many centuries by two bands of indigenous Chinook people— the Multnomah and theClackamas peoples. The Chinook people occupying the land which would become Portland were first documented byMeriwether Lewis and William Clark in 1805. Before its European settlement, the Portland Basin of the lower Columbia River and Willamette River valleys had been one of the most densely populated regions on the Pacific Coast.