Central Park Bridle Path at West 90th Street, next to the Reservoir. There are three bridle paths in Central Park: this one, which goes around the Reservoir, another around the North Meadow, and another in the southern part of the park. They were originally meant for equestrian use, but since the last riding stable in the area closed in 2007[1], they are now used mostly by runners who prefer a softer surface. In 1934, Robert Moses wrote[2]:

The surface of the bridle paths, especially in Central, Prospect, and Van Cortlandt Parks resembled concrete. This material was removed and approximately 21 miles of bridle paths were resurfaced.

This includes the 4¼ miles of Central Park bridle path. Bridle paths were but a small piece of the massive workload of 1934 paid for (as noted in the same document) by "Work Relief Funds" and accomplished with work relief labor[3,4].

References:

1. Gray, Christopher, Whinny if You Miss Central Park's Horses, New York Times, July 5, 2013: “Construction of the bridle paths was a serious engineering project, and in 1860s the Board of Commissioners experimented with the depth of fill, type of rubble, gravel, sand and other materials. The paths were sprinkled in the morning to settle the dust, and raked and rolled at the end of the day. They were treated to as much care as prize rosebushes.”
2. The Report of the Department of Parks to August 1934: Memorandum on 1935 Budget Request of the Department of Parks, NYC Department of Parks archive.
3. Rosenzweig, Roy, and Elizabeth Blackmar, The Park and the People: A History of Central Park, Cornell University Press (1992), p.451.
4. New Deal Assistance in NYC Parks Department Projects, 1934-43.