Grist Mill Trail
The Grist Mill Trail is a paved pathway in the Avalon area of the Patapsco State Park. It is located along the eastern or Baltimore County side of the Patapsco River from near "Lost Lake" upriver to the Swinging Bridge. The paved portion is eight feet wide and there is a 2 to 3 foot gravel horse path, which runs along the length of the trail. The trail is approximately 1.4 miles long and it is "ADA" or "handicapped accessible". The trail makes up a portion of the Patapsco Heritage Trail and numerous historical sites are identified on the PHG trail map.

Grist Mill Trail Extension
The Grist Mill Trail Extension is a completed new section of the trail that runs upriver from the Swinging Bridge to the Ilchester Road in Howard County. This section of trail is approximately 1.1 miles long and extends the existing "ADA accessible" path into Howard County. The extension was completed in Fall 2006 with the installation of a suspension bridge across the Patapsco River at the site of the Patterson Viaduct. The bridge is approximately 200 feet long and is designed for pedestrian and bicycle traffic only.

The southern portion of the trail extension runs generally adjacent to the river and the CSX railroad. The northern portion runs on a portion of the original railbed of the first railroad in the United States. This portion was abandoned when the Illchester tunnel was built. A short piece, near the Bloede Dam, connects the two sections by traversing a slope at 8% or less maintaining the ADA criteria.