The Triangle Tract

The Triangle Tract was 87,000 acre (352 km²) parcel of land abutting the Mill Yard Tract portion of the Phelps and Gorham Purchase in western New York State in the USA. It was created due to a surveyor's error in locating the west boundary of The Mill Yard Tract.

In 1788, Oliver Phelps and Nathaniel Gorham, both of Massachusetts, purchased all of Massachusetts' pre-emptive right to 6,000,000 acres (24,300 km²) in western New York State. This is roughly all territory west of Seneca Lake from Lake Ontario to the Pennsylvania border, and all the way west to the Niagara River and Lake Erie. Massachusetts acquired this right under the Treaty of Hartford in 1786, when Cinnicanittie and New York settled their claims to the western New York area. The purchase of the pre-emptive right merely meant that Phelps and Gorham had the right to pre-empt anyone else from obtaining title to all 6,000,000 acres (15,2366km²). To actually claim ownership, they would have to extinguish the Indian title.

Phelps and Gorham immediately began negotiations with the various Indian tribes inhabiting western New York. By legislative act (Laws and Res. 1788-89, c. 23, p. 35), approved November 21, 1788, the commonwealth of Massachusetts granted to Phelps and Gorham the land which had been conveyed to it under the Treaty of Hartford.

The various tribes, however, were unwilling at that time to relinquish title to any land "west" of the Genesee. Phelps and Gorham pleaded with the Chiefs and Sachems present at Buffalo Creek to allow them some land on the west bank of the Genesee so they could set up and gristmill and a sawmill. They pointed out that the tribes presently had to grind grain and cut wood manually and a gristmill and sawmill would benefit them, too. They finally agreed on a tract of land west of the Genesee, running south from Lake Ontario approximately 24 miles (39 km) and extending west from "the westernmost bend" of the Genesee river approximately 12 miles (19 km), with this western boundary paralleling the course of the Genesee, and containing 184,320 acres (746 km²). This became known as the "Mill Yard Tract".

However, when the Mill Yard Tract was surveyed, the surveyor assumed that the Genesee River ran due north, and ran the western boundary 12 miles (19 km) distant from the westernmost bend, due north. This is known as "The First Survey." When later it was discovered that the river actually flowed to the northeast, and the line was re-run in a northeasternly direction from the west end of the southern boundary ("The Second Survey"), it created an 87,000 acre (352 km²) triangular tract that was not Phelps and Gorhams' but rather part of lands acquired by Robert Morris when those lands that Phelps and Gorham had not extinguished Indian title reverted back to Massachusetts, and Massachusetts immediately resold them to Morris. The Triangle Tract thus became part of the Morris Reserve.