Tualatin Mountains

The Tualatin Mountains (also known as the West Hills or Southwest Hills of Portland) are a range of hills on the western border of Multnomah County, Oregon, United States. 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 Cornell Mountain at 1,270 feet (390 m). Other notable peaks include Council Crest at 1,073 feet (327 m), the highest point in the city of Portland, and Pittock Hill, location of the Pittock Mansion.

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. Human settlement goes back 10,000 years to the area's earliest known residents, the Chinook people.

Despite steep slopes, periodic landslides, and multiple earthquake faults, many residences have been built in the Tualatin Mountains, though much of the northern portion is undeveloped land within the 5,000-acre (20 km²) Forest Park. The landscape, inside and outside the park, is predominantly forested.