1968 when the New York State Office of Parks, Recreation and Historic Preservation had bought a stretch of the Old Croton Aqueduct, for use as a walking trail. It starts in Van Cortlandt Park as a grass-and-dirt trail and runs north along the route of the old aqueduct. The trail features vestiges of an old, disused brick tunnel that brought water to Manhattan, as well as a gatehouse for the aqueduct. Within the park, the Old Croton Aqueduct trail borders Mosholu Golf Center and Driving Range, as well as the Allen Shandler Recreation Area. Its southern end is cut off by the Major Deegan Expressway in the southwestern end of the park. As part of the Croton Water Filtration Plant project, the New York City Department of Environmental Protection was given $200 million to mitigate the effects of constructing the plant. A feasibility study in 2009 found that a bridge near the location of 233rd Street was the most feasible, and would connect the two sections of the trail. This bridge was deferred over lack of funding in 2014 before planning resumed in 2015. The John Kieran Nature Trail (, easy), which connects to the Putnam Trail, opened in 1987 and is named after local writer and naturalist John Kieran. The path features 13 stone pillars, each made of a different variety of stone, that were tested for the facade of Grand Central Terminal during the terminal's construction. The variety eventually chosen was Indiana limestone because it was cheap. The trail hugs the edge of the Van Cortlandt Lake and Tibbetts Brook marsh. The John Muir Trail (, moderate) is the park's only east–west trail that connects the three northern forested areas. It was established in 1997. Various species of trees and flowering plants can be seen along the trail, such as northern red oak, sweetgum, and tulips. There is a large, steep hill in the center of the trail. The Cass Gallagher Nature Trail (, moderate/difficult) is the hardest trail in the park. It was given its current name in 1984, named after a local resident who was a fervent advocate of preserving the park's environment. Shaped as a loop, it extends through the rocky forests of the park's northwestern portion. It was once a "self-guided interpretive nature trail" where hikers could observe natural elements along the trail. Along this trail, there is a "thick undergrowth" beneath a "canopy"