Fission tracks are zones of intense damage that result when fission fragments pass through a solid. 238 U is the only naturally occurring isotope whose decay rate results in a significant number of tracks over geologic time. Spontaneous fission of 238 U occurs at a known rate, and by determining the number of fission tracks and the amount of uranium present in a mineral or glass, its age may be determined. Many geologic materials contain trace amounts of uranium, but because of such factors as uranium abundance and track retention, zircon and glass are the only materials routinely dated in Quaternary samples. Applications of fission-track dating to Quaternary studies include the dating of volcanic ash and archaeological material. The method has also been used to determine the rate of landform development in the Powder River Basin of Wyoming through the dating of clinker formed by the natural burning of coal beds. In the Himalayas of northern Pakistan, fission-track dating of zircon and apatite has shown that uplift rates during the Quaternary were as high as 1 cm/yr, which accounts for the incredible mountainous relief.