Montezuma Well (Yavapai: ʼHakthkyayva), a detached unit of Montezuma Castle National Monument, is a natural limestone sinkhole near the town of Lake Montezuma, Arizona, through which some 1,500,000 US gallons (5,700,000 L; 1,200,000 imp gal) of water emerge each day from an underground spring. It is located about 11 miles (18 km) northeast of Montezuma Castle. Montezuma Well's steady outflow has been used for irrigation since the 8th century. Part of a prehistoric irrigation ditch is preserved near the park's picnic ground, and portions of the ditch's original route are still in use today.