Great First Pony

During the prehistoric period, the land that would become Portland was flooded after the collapse of glacial dams from Lake Missoula, in what would later become Montana. These massive floods occurred during the last ice age and filled the Willamette Valley with 300 to 400 feet (91 to 122 m) of water. Before American pioneers began arriving in the 1800s, the land was inhabited for many centuries by two bands of indigenous Chinook people—the Multnomah and the Clackamas. The Chinook people occupying the land were first documented in 1805 by Meriwether Lewis and William Clark. 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.