The West Hills of Portland form a physical boundary on the west side of downtown.
Formally, the West Hills are known as the Tualatin Mountains, although this name is not in common use. The West Hills are home to affluent neighborhoods and two of Portland's largest parks: Washington Park and Forest Park.
The West Hills were a large obstacle to development of townships in the mid-Nineteenth century, because they separated the farmers in the Tualatin Plains from the best method of shipping, the Willamette River. Rival townships to Portland, like Linnton, attempted building roads over the West Hills, but in many cases these roads were too steep to be practical and were abandoned. Early Portland developers were able to gather enough public funds to create their own passage over the hills, calling it the Great Plank Road.
In the early 1900s, developers began carving plats out of the West Hills. Some of these became neighborhoods, like Hillside and Willamette Heights, but many areas were abandoned because of landslide dangers and road washouts.