October 25: Seattle’s longest mountain bike loop trail opens in Cheasty Greenspace

After more than 13 years of advocacy, the longest forested mountain bike trail within Seattle city limits will officially open Saturday (October 25). The mile-long Trillium Loop in Cheasty Greenspace is a singletrack mountain biking path that travels one-way clockwise through a densely forested and very steep area on the east side of Beacon Hill above Rainier Vista.

The trail is already open, but the official celebration is noon-2 p.m. Saturday at View Point Park in Rainier Vista. There will be a ribbon cutting, family-friendly festivities and, of course, bike riding. UPDATE: Note that e-bikes are not allowed on the mountain bike or shared use paths in Cheasty Greenspace, according to Seattle Parks.

The new trail is by far the longest official mountain bike trail in the Seattle Parks system because, well, it is the longer of the two that exist. It's not even a permanent park feature but rather a three-year pilot project to test the concept of mountain bike trails within city greenspaces. However, the term pilot project" dramatically undersells the amount of community organizing and technical planning that went into this thing. There's a small mountain of environmental studies you can flip through if you're interested in how the path has been designed to consider wetlands and hillside stability. The very steep inclines - often exceeding 40% grades (that's a lot) - are a major reason the space has not been developed into an official park to this point. Of course steep grades are exactly what mountain bike riders are looking for.

When the idea was first proposed, proponents envisioned one big loop trail through the area along with some additional multi-use trails. After extensive study and the help of the trail experts at Evergreen Mountain Bike Alliance, the design evolved into two separate areas each with a mix of single track, shared-use and hiking-only paths. None of the paths would cross the significant wetland between the north and south areas, so riders will need to use Cheasty Boulevard S or S Columbian Way/28th Ave S to get between the two areas. Cheasty Boulevard is an oft-forgotten Olmsted Brothers boulevard from the early 20th century. Though it is not as well-known as its more popular siblings like Lake Washington or Interlaken Boulevards, Cheasty is a stunning and lovely forested road that climbs from Mount Baker Boulevard to Beacon Ave S near the VA. It is also low-traffic, and is the obvious best link between the two bike park sections.

Though the trails are just now opening, volunteers with the Friends of Cheasty Greenspace have been holding work parties for more than a decade to do restorative work in the neglected greenbelt. For example, one of the first things volunteers did was remove large amounts of invasive ivy species that had taken hold and were covering many of the trees. There was also a lot of garbage from many years of people illegally dumping garbage in the secluded forest (this is a thing people do, and I will never understand it). One of the arguments in favor of a mountain bike park was that it is beneficial to people who don't ride bikes because bike riders will be motivated to care for the area and dedicate their time and energy to it.

The other big argument is that the bike trails provide access to mountain biking for folks who can't easily get out to the mountains or Duthie Hill. Kids don't need their parents to own a car and take the time to drive them to the bike park in order to get into mountain biking. Now they can just bike there. The park has great access to transit via several bus lanes and Mount Baker Station, which is located at the base of Cheasty Boulevard just a few minutes away. Anyone within biking distance of the 1 line can now roll their bike onto the train and have access to these trails. There are very few cities anywhere in the world where you can take the local train to go mountain biking.

Development of the trails has also intersected with some less-than-rosy intentions. Amid Seattle's ongoing housing crisis as the city continues to fail to address the core issues of homelessness, the city sweeps people from place to place often destroying their belongings in the process. One obvious result is that people seek out rarely-visited or surveilled areas to set up camps such as greenbelts like Cheasty. Seattle Parks is tracking encampments in the area as part of their quarterly pilot program monitoring reports, and the most recent report (PDF) recorded five encampments during spring 2025. We Heart Seattle, a group often accused of throwing away people's belongings when they are away from their camps, held a cleanup there in June. As with other public and green spaces, the Cheasty area is not a good place for folks to camp (one person famously dug a bunch of tunnels, causing extensive damage the delicate hillside), but people also don't have other good options because we don't have enough affordable housing units or even emergency shelters. Sometimes peeling back the ivy reveals more than a great place for mountain biking.