Tualatin Mountains

The Tualatin Mountains (also known as the West Hills or Southwest Hills of Portland) are a range on the western border of Multnomah County, Oregon, United States.[1] A spur of the Northern Oregon Coast Range, they separate the Tualatin Basin of Washington County, Oregon, from the Portland Basin of western Multnomah County and Clark County, Washington.

The highest peak in the range is Dixie Mountain at 1,609 feet (490 m).[2][1] Other notable peaks include Cornell Mountain at 1,270 feet (390m), Council Crest at 1,073 feet (327 m), and Pittock Hill, location of the Pittock Mansion.[3]

The hills date from the late Cenozoic era, and range up to over 1,000 feet (300 m). Composed mainly of basalt, the mountains were formed by several flows of the Grande Ronde basalt flows that were part of the larger Columbia River basalts.[4] Human settlement goes back 10,000 years[citation needed] to the area’s earliest known residents, the Chinook people