Bristlecone pines are the oldest known living trees, some dating back 4,600-5,065 years old. The age can be found by counting the annual rings in the wood produced. The oldest known individual bristlecone in the world is located in the White Mountains of California and is estimated to be 5,065 years old. Bristlecones can be found in dry, rocky slopes of mountains in the western United States at 7,500 to 11,000 feet elevations, just below tree lines. There are three sub-species, the Foxtail, Colorado or the Intermountain. The foxtail is found in California, in the Klamath Mountains and the Sierra Nevada Mountains. The Colorado or Rocky Mountain can be found in Colorado, northern New Mexico and northern Arizona, while the Intermountain or Great Basin bristlecone can be found in Utah, Nevada, and eastern California. These pines have dark green, very short needles in bunches of 5, bark that is smooth, whitish-gray, which becomes reddish and furrowed with age. They have also been referred to generally as foxtails, as per the look of the needle bunches. The pictures are of the Colorado sub-species, found in northern Arizona.