As Disasters Go, County’s 2 Volcanoes Are Duds : Geology: One hasn’t been active in 16 million years. The other is just a smoky hole in the ground.

After drought, floods, wildfires and a devastating earthquake, what’s next for Ventura County?

Well, did you know about the county’s two volcanoes?

They aren’t much as volcanoes go--one is dead and the other is really just a smoky hole in the ground--but these days, you can’t be too careful.

Some residents may not realize it, but a chunk of mountain near the Conejo Grade, where thousands of cars and trucks whiz by daily on the Ventura Freeway, is the site of a volcano that once disgorged lava with alarming frequency.

And if motorists continue north, they will cruise past what many call the “Rincon Volcano.”

Nestled on a steep hillside north of the Ventura Freeway between the bananas at La Conchita and the surfers at Rincon Point, the “volcano” sometimes startles drivers--and prompts a call to the local fire station--when it emits smoke and fire.

Never mind that the Conejo volcano hasn’t made a peep in at least 16 million years. Or that volcanologists dismiss Rincon’s infamous fire well as a sorry excuse for a volcano.

Because of January’s earthquake, officials have been asked to update plans on how they would respond to a variety of natural disasters. A report by county geologist Jim Fisher does not specifically mention volcanic hazards, but some residents prefer to err on the side of caution.

“That’s all we need, a volcano erupting,” Aaron Foster, 20, of Agoura Hills said as he peeled off a damp wet suit after a morning of surfing at Rincon Point.

“But as long as it doesn’t blow when I’m surfing, I guess it’s OK by me.”

The mouth of the Conejo volcano is under the master-planned community of Camarillo Springs at the northern base of the Conejo Grade. The surrounding area, all the way to Thousand Oaks, sits over a former lava-spewing system called the Conejo Volcanics, Fisher said.

But there’s absolutely no danger of volcanic eruption, geologists agree. The Conejo volcano has been dormant since the Miocene epoch, a geologic period beginning about 24 million years ago.

And it’s not likely to erupt again because the geologic conditions have changed dramatically since then, Fisher said.

“We’re in pretty good shape,” he said. “We’ve got a lot of geologic hazards to worry about, but I would put that one pretty low on the list.”

Of more immediate concern to public safety officials is the so-called Rincon Volcano--which isn’t really a volcano. The formation is actually something geologists call a solfatara, or thermal vent, a place where sulfurous gases escape from a crack in the Earth’s surface.

The phenomenon occurs in Ventura County at a rocky outcropping several hundred feet above the Ventura Freeway between La Conchita and Rincon Point because conditions are just right, geologists say.

The area is composed of shale and is fed by underground reservoirs of oil, said Luke Hall, a geology teacher at Ventura College.

For some reason--perhaps a spark caused by rocks shifting in the ground--the fissure spontaneously ignites and begins burning off the oil, Hall said. When air invades the chamber and the rocks are very hot, the burning starts to accelerate, he said.

What most people see are steamy gases creeping from the side of the mountain, he said.

On foggy days, the steam looks like smoke, Ventura County Fire Chief George Lund said. That sometimes prompts drivers to pull over and report a fire, he said.

“It’s a continual nuisance for us,” Lund said. “Our Rincon station gets calls on it a couple of times a year, and we always have to check it out just to make sure it’s not a real fire.”

People calling tend to get excited by what they see, he said.

“They see smoke, and smoke is fire to most people.”

The first recorded report of the “steaming mountain” was made in 1835 by a man traveling north by stagecoach to La Purisima Mission in Lompoc, said David Griggs, curator of the Carpinteria Valley Museum of History.

Since then, several sightings of vent activity have been made. But it is impossible to predict when the Rincon Volcano, now quiet, will again begin to smoke, Hall said.

“It seems to subside when air is cut off,” he said. “Someone told me it was smoking a lot in the ‘50s.”

Bobette Bates McKay, whose family owns the 400-acre ranch where the vent is, said locals dubbed the formation the Rincon Volcano because it sometimes spewed fire along with gases.

As children, she and her brothers and sisters did a lot of exploring on the ranch and they just took the volcano for granted, said McKay, 74.

“I never went down to the mouth of it, but my younger brother did,” McKay said. “I probably didn’t want to get my clothes torn.”

The vent sometimes flared up at night, creating a spectacular natural Bunsen burner. But invariably it only lasted a day or two before dying down, she said.

“It was seldom that we saw it,” McKay said. “It was fun for a day or two, but that was about it.”

Fisher said there are similar rock formations near Grimes Canyon Road south of Fillmore. But people don’t see them because they are buried in old mines, he said.

The Conejo volcano, on the other hand, is visible to anyone who drives over the Conejo Pass. But most people don’t realize that they’re looking at the main vent from magma upwellings that formed the Conejo Volcanics.

“I wasn’t aware of it,” said Martha Beckman, who sells houses in the Camarillo Springs development that sits right on top of the neck of the volcano.

“But it doesn’t surprise me. Nothing surprises me any more after all the disasters we’ve had.”

The volcano was probably most active about 16 million years ago when it was covered by the ocean, Hall said. Tectonic activity since then has caused the volcanic chain to be uplifted and tilted on its side, forming the western end of the Santa Monica Mountains, he said.

That movement effectively capped the volcano, and it is not likely it will again erupt, Fisher said. At least not during our lifetimes, he added.

“The tensions that create volcanoes are no longer there.”

In addition to Camarillo, remnants of the volcanic ridge cover a wide swath of the eastern county, including all of Newbury Park and parts of Thousand Oaks.

Residents seemed to take news of the volcano in stride.

Bert Vanacker of Newbury Park said he didn’t learn about the volcano until after he bought his home a decade ago. The retired water and power worker said he doesn’t give it much thought, though.

“It’s not an item I would ask about if I was going to buy a house,” he said. “A volcano? I think you just have to take your chances and, if something happens, you just do the best you can.”

Ventura County’s Volcanoes

Ventura County has two “volcanoes.” The Rincon Volcano is actually a geiser-like geologic formation that spews vapors from a steep hillside above Highway 101 near Rincon Point. The Conejo Volcanics in the eastern county is a dormant volcanic ridge that last erupted hot molten magma about 16 million years ago.