Casa Grande is the most prominent remnant of an ancient civilization that occupied the Salt and Gila River valleys from A.D. 300 to 1450. Archeologists call these people Hohokam, a Pima word meaning "those who are gone." The Hohokam were farmers well adapted to desert living, and irrigation was the key to their farming. With simple tools and manual labor, they dug hundreds of miles of canals and maintained extensive trade routes in all directions, receiving goods from hundreds of miles away. The first European to observe the ruins was Father Kino, a Jesuit missionary, who visited in 1694, when Casa Grande, or Big House, had already been abandoned for over 250 years. What happened to the Hohokam is not known. Some archeologists believe they are the ancestors of present-day Indian groups, while others believe they gradually left the area because of flooding, decreasing soil productivity, a breakup of trade routes, or some combination of these and other events. Much remains unknown about the Hohokam, and even the purpose and use of Casa Grande are uncertain, though some of its features suggest it was an observatory, the dwelling of a village leader, or a religious building.