The 3.5 mile Ridley Creek Trail provides the shortest access to Mount Baker from Bellingham, but it is it isn't well-known for two reasons: first, it has been abandoned for years, which means deadfall is a big problem, and continuing more than a quarter mile from the trailhead requires crossing the Middle Fork Nooksack River.
Fortunately, this forgotten trail came under the radar of WTA, and reconstruction started in the fall of 2014. However, the river crossing remains a problem unless a footlog is in place (As of 2014 there was one at N 48 43.594 W 121 53.819).
You do not need to cross the river to access this cache, but I highly recommend at least continuing down to the riverbed. Only a couple miles downstream from the Deming Glacier, the gravel bars provide an excellent view of Mount Baker!
After crossing the river, the trail switchbacks up to Mazama Park, where it joins with the Bell Pass Trail about a mile below Park Butte Lookout. You can even combine this trail with the Bell Pass Trail, Elbow Lake Trail, and part of the Middle Fork Road to make a giant loop!
The cache is accessed by driving the Middle Fork Rd (which is accessed of of the Mosquito Lake Rd) to its very end at (N 48° 43.570 W 121° 54.104). The road is gated at (N 48° 44.766 W 121° 56.794) from December 1 - June 15, which will add 5mi RT onto your hike. The container is a lock-and-lock.
Happy Hunting!