One theory is that the massive amount of shellfish remains represent Ohlone ritual behavior, whereas they would spend months mourning their dead and feasting on large amounts of shellfish which were disposed of ever growing the girth and height of the mound. Shellmounds were once found all over the San Francisco Bay area near marshlands, creeks, wetlands, and rivers. San Bruno Mountain is home to the nation's largest intact shellmound. These mounds are also thought to have served a practical purpose as well, since these shellmounds were usually near waterways or the ocean, they protected the village from high tide as well as to provide high ground for line of sight navigation for watercraft on San Francisco Bay. The Emeryville Shellmound is a site standing at over 60 feet (18 m) tall and 350 feet (105 m) in diameter, and was believed to be occupied between 400 and 2800 years ago.