PDX Runs: Mary S. Young Park
Right off of Hwy. 43/Willamette Drive in West Linn is 130-acre Mary S. Young State Recreation Area. Mary S. Young is a mostly wooded park, with a few miles of trails, as well as ball fields, a dog park, and a rocky beach on the Willamette River.
As the story goes, a Mary Hoadly Scarborough Young of Lake Oswego purchased the property as a gift for her husband, and when he turned down the extravagant present, she left it to the state. The park was dedicated in 1973.
Most of the trails in the park are bark-chipped and pretty short, but string them together, and you can make a nice run and escape the city for a bit.
The Heron Loop Trail (1.6 miles) is the longest trail in the park. Extend it via a couple others, including some of the paved Riverside Loop, and you can circumnavigate the property over the course of about 2.25 miles.
The city of West Linn, which operates the park, has a nice map right here.
Mary S. Young park has all the amenities a runner could need: parking, bathrooms, and water fountains. The main entrance is at 19900 Willamette Dr, West Linn, OR 97068.