The trail uses the old right-of-way of the Bellingham to Mt. Vernon Interurban Line which operated from 1912 to 1930, and the trail is a cooperative effort of the city, county, state park, and Puget Power Company. It was dedicated in 1987 and runs over 8.5 miles, from Bellingham to Larrabee State Park.
I began the ride from the ferry parking lot and found a gravel connector trail which runs behind businesses and crosses all the side streets east of the downtown area and the ferry terminal. A parking area is available along Fairhaven Parkway (I-5 Exit 250). Access to the trail is also available from the state park. This map below is available as a .pdf here.
The historical perspective is provided by this sign.
The trail passes through lovely woods and has some serious up-and-downs as it works its way over two hills, some steep enough to require many to walk sections (just consider walking your bike as cross-training!) As you get closer to the state park, the trail is on a ledge several stories above the highway, and briefly shares the right-of-way with vehicles in a residential area.
The trail is lovely as is obvious from these photos. Rain is not a problem here, and the lush vegetation seems to close in on you in a good way, embracing and welcoming you, not threatening you.
Small creeks are bridged to preserve the environment and keep you dry. Obviously the thick foliage reduces sight lines in areas like these, so bike sensibly to avoid collisions.
On the bottom of the map below, the trail's route begins to the right of the "N" arrow, and the trail is the black line which makes a modified "S" curve to the state park at the top.