Spring water spurts out of rocks and trickles down the moss- and vine-covered cliffs in Solano County's Green Valley - an oasis in a canyon that was parched by drought only two weeks ago.

That was before Napa's magnitude 6.0 earthquake.

It turns out that the earth's mighty shifting - which caused about $400 million in damage to Napa, Sonoma and Solano counties - also mysteriously forced groundwater to the surface and into several dry or nearly dry creeks and streams in the region.

"This was never wet before," said Mark Witherspoon, the reservoir keeper for two of Vallejo's key sources of water, Lakes Madigan and Frey, as he stood amid a steady cascade of water in spectacular Green Valley canyon and pointed out a bubbling, burbling fissure.

Torrents of water have been flowing down Wild Horse and Green Valley creeks and another unnamed waterway in the hills southeast of Napa and northwest of Vallejo since the Aug. 24 quake.

Great for Vallejo

It is a potential bonanza for drought-plagued Vallejo, which built an emergency pipeline from Lake Berryessa in the spring after officials learned that their supply of Sacramento-San Joaquin River Delta water was being cut off. The liquid infusion, which some locals have taken to calling "miracle water," bubbled up within the 1,500-acre watershed that Vallejo has exclusive rights to use.

"This is an unusual thing to have happen," said Franz Nestlerode, the assistant public works director for water in Vallejo, in a tone indicating he could barely believe it himself. "Potentially it could turn out well for us."

Solano County isn't the only place getting an unexpected dousing. At least four other mostly dry waterways in Sonoma and Napa counties have seen big surges of water since the quake, according to geologists.

"This phenomenon is commonly reported after earthquakes," said Tom Holzer, a hydro-geologist with the U.S. Geological Survey.

He said earthquakes can cause fissures in the rock that bring up groundwater. He has received reports since Aug. 24 of similarly dramatic increases at Tucolay Creek east of Napa, Carriger Creek near the city of Sonoma, and two unnamed creeks, one in Doak Canyon and the other just north of the Oakville Grade. The U.S. Geological Survey measured a 20-fold increase in one Sonoma creek.

Holzer said he would be surprised if there aren't other creeks and tributaries in the area that have also become engorged with water.

Vallejo's water treatment plant is on Wild Horse Creek, which is fed by the Madigan and Frey reservoirs, about 2 miles upstream. The city normally mixes the reservoir water with contracted water from Lake Berryessa and then pipes the treated drinking water to Vallejo residents.

After the earthquake surge, city officials quickly shut off the flow from the reservoir, but water continued spilling over the district's diversion dam, built between towering cliffs in 1896.

Increased daily flows

Nestlerode said at least 200,000 gallons of water a day are flowing down Wild Horse, which joins Green Valley Creek before emptying into San Francisco Bay. He said the natural flows were about a tenth of that before the earthquake. Sporadic releases from the dams amounted to at most 100,000 gallons day, he said.

Witherspoon and fellow reservoir keeper Tim Lindemann frantically checked the Madigan and Frey dams for cracks, leaking pipes and other irregularities after the quake, but could find nothing. Subsequent inspections by the California Department of Water Resources dam safety division of the seven reservoirs maintained by the city of Vallejo found no leaks, breaches or cracks, Nestlerode said.

They then noticed that the creek was dry for about a mile below the dam before water began spurting out of the rocks, down the canyon walls and up from the creek bed.

Holzer said scientists have known about this phenomenon since at least the 1860s. Surging water was reported in several creeks after a 7.3-magnitude quake in Kern County in 1952. Geologists long believed the water was being squeezed up through Earth's crust. That all changed in 1989 when the Loma Prieta Earthquake caused tenfold increases in flows in the San Lorenzo River and Pescadero Creek.

Cracks in the rocks

"What we concluded is that it was shallow groundwater and that the shaking had been sufficient to open cracks and fissures, increasing the permeability of the rock and allowing the water to flow faster through the cracks," Holzer said.

Testing of the Wild Horse water supports Holzer's contention. The samples showed relatively high alkalinity, Nestlerode said, indicating groundwater. He is currently letting the new water flow out past the treatment facility while he waits for laboratory tests to determine whether there are heavy metals or radio nuclides in the water.

"We'll use it if the tests come back in a couple of weeks and everything checks out," he said.

Alas, said Holzer, Vallejo would be best served if they don't bank on the extra H2O.

"Usually in a few weeks, maybe six to eight weeks, the creeks return to normal," he said. "There is only so much water in there. As the water table lowers, the water flow diminishes. It's like a bank account. You've just reached into the bank account and borrowed some money, but the spending spree will eventually end."

And, he said, the liquid largesse could eventually have negative consequences.

"It's an indication that the earthquake has changed the shallow groundwater system," Holzer said. "So people who have wells in the area, particularly if they are shallow wells, could find their wells going dry. That actually happened in the Loma Prieta quake."

Nestlerode, who is retiring in a month, is aware that Mother Nature's charity may stop, but he refuses to dwell on the negative.

"You never really know with certainty," he said. Either way, "it's been a busy last year on the job with the drought and now this. I'll have stories to tell."

Peter Fimrite is a San Francisco Chronicle staff writer. E-mail: pfimrite@sfchronicle.com Twitter: @pfimrite