Tripod Rock is a glacial erratic,[1] in this specific case a balancing rock,[2] or perched boulder, located in Kinnelon, New Jersey in the Pyramid Mountain Natural Historic Area. This multi-ton Precambrian gneiss boulder, located near the edge of a long ridge, is balanced on three smaller boulders. Tripod Rock is roughly long, wide, and high, weighing approximately 127tonnes. A triangular crest runs the length of its top. The boulder is balanced on three smaller stones roughly in diameter that raise it above the bedrock by about at its lowest point. The point of contact between the boulder and its support stones forms an approximate 3-4-5 triangle.
About northwest of Tripod Rock are three other boulders comprising a triangle. The two larger boulders are partially balanced on smaller stones (see diagram). The apex rock is about to the northeast. Two smaller perched boulders are located northeast of Tripod Rock (not shown on diagram) measuring approximately in diameter. No specific calendar alignment has been noted. Tripod Rock stands on a ridge overlooking a long valley where a massive glacial erratic named Bear Rock is located near a brook. Bear Rock was thoroughly excavated for archaeological artifacts during the 19th century, some of which are reported to be owned by museums. Bear Rock has a large overhang making it a possible rock shelter.