Six hundred years before cigarettes were sold at Pleasanton's Safeway, much earlier Californians were smoking tobacco in the same area.

UC Davis researchers have found nicotine in ancient pipes excavated from an Ohlone burial site in Pleasanton at the corner of Bernal Road and Highway 680, a discovery that deepens the history of humans' long relationship with tobacco.

The find also sheds new light on the lives of local Native Americans -- suggesting that they were gardeners, nurturing small patches of precious plants, not just restless hunter-gatherers.

"The antiquity of tobacco smoking" among western North American tribes "was, until now, completely unknown," said Shannon Tushingham, a UC Davis archaeology research associate and lead scientist on the project.

"There was something special about this plant," she said. "Now it is used by hundreds of millions of people."

Archaeologists have long known that tobacco played an important role in ancient South and Central American tribal culture. Then it spread into eastern North America 2,000 to 3,000 years ago.

But the history of its introduction and spread into western North America has been as hazy as its smoke.

A sophisticated analysis of residue revealed nicotine in a Pleasanton area pipe was smoked between 1350 and 1400.

Older evidence of nicotine was found in six pipes dating back to 860 discovered during excavations of a village that is part of the homeland of the Tolowa people, near Crescent City on the Northern California coast.

Because tobacco is native to arid deserts but not the coast, its cultivation may have meant the preparation of plots, sowing of seeds and watering, said Tushingham.

The Pleasanton site was discovered during excavation of the 39-acre shopping center in 2011. Archaeologists removed the remains of 187 people from well-prepared graves; another 470 graves were found on adjacent land developed as a housing tract.

The site, in the rich watershed of Alameda Creek, is believed to have been occupied continuously from 1000 until 1650. The remains -- and the pipes -- have since been reburied. Researchers, fearing vandalism, did not disclose their current location.

One pipe was found near the skull of a young man. Pieces of another were found with the cremated remains of a second person.

Both pipes were carefully drilled to create a tubular shape, about 5 inches long. One is sandstone; the other is soapstone, or steatite.

"They were skilled craft workers," said UC Davis archaeologist Jelmer Eerkens, another member of the team. Because the stone is not found on the property, the pipes must have come from elsewhere, he said. These tribes were part of a large trading network.

The early tobacco had a lower nicotine content -- less than 2 percent -- than today's tobacco, which has 4 to 8.5 percent, the researchers said. Tobacco was likely saved for special ceremonies rather than widespread and habitual use.

Sensitive gas chromatography and mass spectrometry tools, made by Santa Clara's Agilent Technologies, identified the chemical "fingerprint" of nicotine.

More chemical analysis may help push the antiquity of tobacco use even earlier, and could help track the spread of the plant through the Americas, the team said.

Contact Lisa M. Krieger at 650-492-4098.