[3] 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.

[4] Human settlement goes back 10,000 years[citation needed] to the area's earliest known residents, the Chinook people.

[citation needed] U.S. Route 26 (the Sunset Highway) is the principal transportation link through the hills, traveling through the Vista Ridge Tunnels, Tanner Creek Canyon, and over the crest of Sylvan Hill.

This route through the hills connecting the agricultural Tualatin Basin to the navigable Willamette River was developed as a plank road in the 19th century.

Since 1998, the west side MAX Light Rail has run roughly parallel to US 26 through the hills, including a section tunneled deep underground.