Rio Nuevo dig yielding "layer cake" of history, prehistory

Archaeologists are having a field day with their trowels, scraping away layers of dirt just outside what was the outer wall of the Mission San Agustín.
Three weeks of excavation uncovered 2,000-year-old arrowheads. These lie a few feet from the first mission-era American Indian home discovered in Tucson, and they're only a few feet away from a 1930s barbecue pit.
"I can't think of anywhere in the United States where you have this layer cake of cultural change," said Michael Brack, project director at Desert Archaeology, which is doing the dig.