Casa Grande Ruins National Monument, the first archaeological reserve in the United States, is a testament to the Hohokam Culture's Indian's social organization and engineering skill. Built by this prehistoric farming community around A.D. 1350, the Casa Grande or Great House stands four stories high and measures 60 feet (18 meters) long making it the largest known Hohokam structure. But the importance of this Arizona archeological site goes beyond size. Archaeologists believe that by the time Casa Grande was erected Hohokam social and rel... Read Moreigious authority was centered in a few select villages. What's more, archaeologists think that the Casa Grande served an astronomical purpose. Casa Grande's four walls face the cardinal points of the compass and, at specific times of year, holes in three of the four walls align with the moon and sun. So why did the Hohokam abandon Casa Grande? Severe flooding in A.D. 1355 is believed to have provoked a crisis in the Hohokam community that led to a slow societal collapse. From A.D. 1355 to 1450 small groups moved into the desert one at a time.