Geology of Fort Tryon

The site for Fort Tryon Park is magnificent, on some of the highest open land in Manhattan, with views in all directions: to the west, of the river and Palisades; northward, of Inwood Hill and the river towards Tarrytown; southward, of the river towards the George Washington Bridge; and eastward, of Inwood and the Bronx. It was, however, a site that was basically difficult to adapt for use as a public park, with its steep rocky topography and thin soil. Olmsted Brothers created an outstanding park design which, true to the Olmsted legacy, respected the uniqueness and natural landscape possibili­ties inherent in the site. This design recognized that the primary function of the park was as a “landscape park occupying a site of extraordinary land­scape interest, “16 a preserve of open land with spectacular views of the Hudson River, that was therefore to be used for “passive” recreation (except in one location on low ground at the northern edge of the park where a play­ground was placed). A secondary function was as the setting for the Cloisters, which Rockefeller wished to be the “culminating point of interest in the architectural design of the park. “17 Within these overall purposes, the park was designed to present a variety of landscape experience. As stated by Olmsted, Jr., in his preliminary report of 1927: – LPC (First paragraph of page 8)

The steep topography dictated many of the design decisions and features of the park. Stone retaining walls with parapets were employed extensively to re­tain soil as well as to keep pedestrians on the paths. The wooded slopes were an artful arrangement of the natural and artificial, with the addition of soil, rockwork, and extensive plantings to existing vegetation and rock forms. The relatively few flat areas available were reserved for the creation of small open lawns bordered by trees. – LPC (Third paragraph from page 8)

Construction work by Olmsted Brothers, which began on Fort Tryon Park in August 1931, required a variety of procedures: demolition of the Billings mansion and stables; extensive rough grading of the site; layout and con­struction to sub-grade of the roads and paths with their retaining walls and parapets; construction of rock-filled slopes; construction of masonry arches, terrace and overlooks, wading pool and various structures; preparation of planting beds and lawns with loam and fertilizer; and planting of trees, shrubs, herbaceous areas and lawns (including the transplanting of some 180 mature tress on the site to avoid their destruction). A deep cut was made into the ridge of rock facing the Hudson River in order to build a drive which connected the park with Riverside Drive. The 36,000 cubic yards of gray Manhattan schist that were removed were, employed in the construction of the architectural elements of the park, and a great deal of care went into the quality of the masonry. A workforce averaging 350 men worked on the site daily, under the supervision of Edward J. Carillo, Superintendent in Charge of Construction for Olmsted Brothers. Construction work was performed by the Arthur J. Johnson Corp. under contract with Marc Eidlitz & Son, General Contractors. 13 During construction, artifacts of the Revolutionary War were uncovered. The park as constructed was a refined version of the original preliminary general plan. A small parcel of land along Broadway from Bennett Avenue to West 196th Street was added to the park in 1933 through a gift of J.D. Rockefeller, Jr. – LPC (first paragraph page 7)

The artful Olmsted Brothers’ design and Fort Tryon’s rocky features are easily accessible from the network of paths that traverse its steep slopes and wind through its open meadows and wooded areas making it seem much larger than its 67 acres.

Glacial potholes and striations, faults, and varieties of schist are among Fort Tryon’s many geologic features created during the last glacial period that ended more than 12,000 years ago. The rocks of Fort Tryon may be between 565 and 450 million years old.  Here are a few of the most notable geologic features:

  • At the northern end of the park, above Anne Loftus Playground in one of the massive rock outcroppings that are prominent in the park, sits New York City’s largest glacial pothole. Today, only half of the pothole remains because during the initial construction of the park, the other half was blasted away to create the pathway.
  • Glacial striations or scrape marks can be found on many rock surfaces throughout the park including those found in the Heather Garden. These were formed as the mile-high mass of ice embedded with rocks advanced from the north exerting immense pressure on the Manhattan schist. Smoothness, also notable in the rock, indicates glacial polishing by the rock particles in the glacier.
  • North of Fort Tryon, the Dyckman Street Fault appears as a low-lying area. But geologically, it marks the site of a fracture in the bedrock of northern Manhattan. Faults are often the sites of seismic activity, but no activity has been reported in historic times in this area. Beneath the low-lying areas surrounding the park is the weaker Inwood Marble.
  • Manhattan schist appears in several forms in the park. This metamorphic rock is formed of mud from the sea floor that was transformed and recrystallized by profound heat and pressure; it is categorized by its mineral content. Mica schist looks like it contains small shards of a broken mirror, and garnetiferous schist is peppered with tiny crimson garnets.

Fort Tryon is replete with rocks imported from other areas. The curbing is from Stony Creek, Connecticut. The blue stone paths are from the Catskills. The granite on Billings Terrace came from Deer Island, Maine, while the granite of The Cloisters is from New London, Connecticut.