The Joshua tree is native to southwestern North America, in the states of California, Arizona, Utah and Nevada. Confined mostly to the Mojave Desert between 400-1,800 m (2,000-6,000 feet), they thrive in the open grasslands of Queen Valley and Lost Horse Valley in Joshua Tree National Park. Joshua trees can grow from seed or from an underground rhizome of another Joshua tree. They are slow growers; new seedlings may reach a height of 10-20 cm in their first few years, then only grow about 10 cm per year thereafter. The trunk of a Joshua tree is made of thousands of small fibers and lacks annual growth rings, making it difficult to determine the tree's age. This tree is not very sturdy because of its shallow root area and top-heavy branch system, but if it survives the rigors of the desert it can live to two hundred years of age. The tallest trees reach about 15 m tall. The Cahuilla Native Americans who have lived in the southwestern United States for generations still identify with this plant as a valuable resource and call it “hunuvat chiy’a” or “humwichawa”. Their ancestors used the leaves to weave sandals and baskets in addition to harvesting the seeds and flower buds for nutritious meals. The name Joshua tree was given by a group of Latter-day Saints who crossed the Mojave Desert in the mid-19th century. The tree's unique shape reminded them of a Biblical story in which Joshua reaches his hands up to the sky to stop the sun by God's command. Ranchers and miners who were contemporary with the Mormon immigrants also took advantage of the plant, using the trunks and branches as fencing and for fuel for ore-processing steam engines. There is some concern that Joshua trees will be eliminated from Joshua Tree National Park due to climate change, and that this will damage the ecosystem of the park. There is also concern about the ability of the trees to migrate to favorable climates