National Trails Day is June 6, 2020.
According to American Hiking Society, “Taking place on the first Saturday in June, National Trails Day® is a day of public events aimed at advocacy and trail service. Thousands of hikers, bikers, rowers, horseback riders, trail clubs, federal and local agencies, land trusts, and businesses come together in partnership to advocate for, maintain, and clean up public lands and trails.”
You can register a trail event for National Trails Day–and even get empowered to invite your local reps to join you–via the National Recreation and Park Association here.
Official registration for 2020 events begins February 2020.