But archaeologists have long suspected that a different crop, the lowly manioc plant, was the mainstay of Maya life, providing the basic sustenance that allowed their civilization to flourish in densely populated cities. Now, Colorado researchers have provided the first direct evidence that manioc was indeed intensively cultivated by the Maya -- in quantities that would allow its use for many different purposes. Manioc, also known as cassava, grows into tubers as much as 3 feet long and as thick as a human arm and produces the highest yield of food energy for any cultivated crop, about eight to 10 times as much as corn. It can also be grown in infertile soils and requires little or no irrigation. The newly discovered manioc fields are in the El Salvadoran village of Ceren, about 15 miles west of San Salvador. An eruption from a vent in the nearby volcano Laguna Caldera on an August evening in A.D. 590 buried the village under as much as 17 feet of ash. The village, which housed 100 to 200 residents, has been called the 'American Pompeii' because of the remarkable preservation of artifacts. So far, archaeologist Payson Sheets of the University of Colorado and his colleagues have excavated 12 buildings, including houses, a sauna and a religious gathering place. All of the inhabitants appear to have escaped, perhaps warned off by an earthquake that preceded the eruption. In their initial investigations around 1990, the scientists found evidence that the residents consumed cacao, tropical fruit, seeds and berries, deer, ducks and snails. Two years ago, in their first excavations outside the village proper, they found manioc in one pit. 'The big question then was, was this one small field which we were fortunate to hit?' Sheets said in a telephone interview Friday. When the team returned to the site in January, they dug 18 large test pits, each measuring about 10 feet by 10 feet. 'We found two boundaries, the east and west, but not the north and south boundaries,' Sheets said. The area of the field exposed so far is about one-third the size of a football field and would have produced about 10 metric tons of manioc annually. They did not find the manioc, of course. What they found were empty spaces once occupied by the plants before they disintegrated. The team injected these holes with dental plaster before excavating carefully around them, revealing a cast of the remains of the crop -- which had just been harvested -- and stalks that had just been planted to produce the next season's crop. The next big question is, what were the villagers going to do with so much manioc? The tubers will normally rot in three to four days. They can, however, be peeled, cut up into chunks and dried in the sun for eight days before being ground into a flour called 'almidon,' which can be stored for long periods. Almidon can be added to soups and stews to increase carbohydrate content and used to make tortillas and tamales. The manioc can also be fermented into a beer that was used in Mayan festivals and celebrations. Sheets said he and his students will brew some in pots that he had specially made, then examine the pots to see what kind of residues are left in the clay. The team will then examine pottery they have previously found at the site to search for the same residues. 