Turquoise, or "Sky Stone", is iconic for its use in Native American jewelry. For hundreds of years, native people in the Southwest used turquoise for ornamental and religious purposes. The Cerrillos Hills in New Mexico are riddled with prehistoric turquoise mines, possibly dating back as early as the first century CE. American Turquoise is mined in Arizona, Colorado, Nevada, and New Mexico, with Arizona and Nevada being the largest producers. Arizona turquoise is known for its blue color. The presence of copper creates these deep blue tones. Nevada turquoise is better known for its green colors, with higher levels of iron and zinc causing this effect.