The Hohokam, the ancestors of the Akimel O'odham (Pima), constructed the Mesa Grande temple mound. With walls made from "caliche," the calcium carbonate hardpan that forms under our desert soils, the mound is longer and wider than a modern football field and is 27 feet high. Construction of the mound began by AD 1100 and continued to at least AD 1400. A large adobe wall encloses the mound and a large plaza in front of the mound. In one corner of the site, volunteers from the Arizona Museum of Natural History constructed a replica of a Hohokam ballcourt, an open-air structure where ballgames were played using a rubber ball made from a local plant. The City of Mesa purchased the Mesa Grande ruins in the 1980s to preserve Mesa's premier cultural treasure and to open it to the public as an educational and recreational facility. Open from mid-October to mid-May.