Pioneer park is not primarily used for mountain biking, although some do run the trails. The northwest quadrant is basically level, with lovely trails meandering through the woods. A horse trail runs along the eastern edge of the park. It is it acceptable to have off leash (but under voice command) dogs in this quadrant. The northeast quadrant is leash only, has some hills, and has access to Lake Washington. The southeast quadrant is also off leash, is somewhat hilly, and all trails are open to horses. The southwest quadrant has a stable and retail stores. Great park, we go daily!