The Willamette Valley is the Oregon region surrounding the Willamette River as it proceeds from south of Eugene, Oregon down river (and north) to Oregon City. In common use the valley ends when it reaches the urban growth boundary of the Portland metropolitan area; based on physical geography, the valley continues through the middle of Portland until it meets with the Columbia River. Its western boundary is defined by the Coastal Range; its eastern, by the Cascade Range. The Willamette Valley is home to nearly 20% of Oregon's population (or 60% if the Portland area is included). It was also the destination of many who traveled the Oregon Trail. The valley forms one of the most productive agricultural regions in the world. For example, it produces most of the grass seed sold in North America. It has also become a major wine producer, with an AVA of its own. With a cooler climate than California, the gently rolling hills surrounding the Willamette are home to some of the best pinot noir in the New World, as well as a high-quality pinot gris. The valley includes three entire counties: Benton, Polk, and Yamhill,as well as parts of four others: Clackamas, Lane, Linn, and Marion.