Tolt Pipeline Professional Review and Guide
"The Tolt Pipeline is a 100-foot-wide, 12-mile-long trail for foot, horse, and bicycle use. The Seattle Water Department built the pipeline in 1963 to bring water from the Tolt River Reservoir to the city. It acquired a strip of land 100 feet wide and, with the help of King County Parks, established the 12-mile route as a park. It has great steep hills, dirt and gravel surfaces, and runs from Bothell to the Snoqualmie River Valley. The trail is well maintained and there is enough traffic that it’s safe to run alone. This is a great place to develop your hill running muscles without having to worry about the tricky footing on mountain trails.
The main drawback is that it crosses several major roads, including Interstate 405, if you take it all the way from Blyth Park. The section described here leads from the Sammamish River to the Snoqualmie Valley in about 8 miles, all of it runnable. This section is mile 4 through 20 on the elevation profile and gives you 16 miles out and back. However, the profile also includes the section west of the Sammamish River. I’m thrilled by the fact that you can get from the heart of Seattle to the Columbia River on a network of trails and this is one of the links."