A small pine tree, approximately 15-40 feet (5-13 m) high, which is the oldest living tree in the world. It is native to the Rocky Mountains of the United States, at elevations above 7,500 feet (2,300 m), and they have the longest life-span of any conifer. A stand of this tree in eastern Nevada is known to have several trees over 3,000 years old, and one of them is thought to be about 4,900 years old. The combination of these and some well-preserved dead examples have allowed a dendrochronological key to be built, has changed some of the assumptions underlying radiocarbon dating, and has provided calibration for radiocarbon dates going back about 7,000 years.