Much older.

This majestic rolling range at the foot of Mount Diablo provides more than soothing vistas and pricey real estate. The ancient hillocks, which rose up millions of years ago, are signposts of the past for scientists. Researchers aren't precisely sure what the Bay Area looked like 10 to 15 million years ago. But new sedimentary evidence - something like a prehistoric Thomas Guide - is giving them a pretty good snapshot.

You would hardly recognize the place back then. It was relatively flat, much like the Mississippi delta. There was volcanic activity in the Oakland-Berkeley hills.

"The topography has been reversed" observes Anna V. Buising, associate professor of geology at Cal State Hayward. " The highs are low and the lows are high. It's called topographic inversion".

Many of the Earth's secrets are found on high ground. To get there, Daniel W. Dunn, who leads volunteer digs at an ancient Blackhawk stream bed, slips his blue GMC Suburban into low gear, plows through shoulder-high thistles and charges up a steep hunchback hill. The vehicle sways over rough terrain.

Tucked amongst these foothills is one of the most important West Coast dig sites for the late Miocene period. What is now the Blackhawk Ranch Fossil Quarry was created about 10 million years ago by fast-moving waters and seasonal floods that swept up dead animals from around the region. Over time, the river bend collected bones like pieces of a puzzle. Water eventually stopped flowing, but the animal detritus remained in the sandbar.

The dish-like quarry is accessible only by strenuous hike or, in this case, via four-wheel drive. Officials do not want the site's location mentioned for fear of fossil thieves, who have already raided it.

"The site is so rich" says Dunn, director of operations at The Museums at Blackhawk. He leads volunteer summer digs at the quarry, which is operated by the UC-Berkeley Museum of Art, Science and Culture. "I have never had anyone not find anything here. It's rewarding to see someone holding a 10-million year-old fossil. You almost can see the lights come on".

Like a Savanna

Eleven hundred feet below are homes of the wealthy, in an area once wooded and populated by very different residents.

"you're talking about animals that don't even exist in North America anymore walking around in our backyards," Dunn says.

"It would have resembled to some extent and African savanna, " observes Howard Hutchison, a UC-Berkeley research paleontologist emeritus. "You had rhinoceros, camels, horses - various carnivores."

Mount Diablo - no, it wasn't a volcano - was a geological molehill under the ancient San Pablo Bay. (Volcanic material found on the mountain today actually was part of the ancient sea floor.)

And San Francisco was probably under water with the fish. The San Francisco Peninsula was possibly an island. In fact, the entire Bay Area did not rise above sea level until about 6 million years ago.

Still, parts of the East Bay were teeming with wildlife 10 million years ago. "contra Costa was a happening spot, and Alameda too," Buising says. "The Peninsula as we know it didn't exist. In fact, all of the landscape of the Bay Area as we know it is young, geologically speaking."

Humans are even younger - "just a cosmic eye blink," she adds. They did not arrive until quite recently, between 10,000 and 11,000 years ago.

Long before people came on the scene, the Mount Diablo region had an undulating landscape with woodlands hugging streams. Researchers have found fossil leaves from numerous trees, including poplars, willows, oaks, elms, sycamore, mahogany and sumac.

"it was probably a warm climate" says Jere Lipps, director of the UC-Berkeley Museum of Paleontology. "But it wasn't as hot in the summer or as cold in the winter. It was pleasant. The rainfall is said to have been 25 inches spread over the year."

Rapid Change

Geologists have been studying the region for 100 years. But they still don't have a clear picture of what the Bay Area was like millions of years ago. The Pacific and North American plates have rubbed against each other for eons, re-arranging the Bay Area landscape like a waiter changing table settings. From a geological perspective, change came fairly rapidly.

"The whole place has been shredded and shuffled," says Janine Weber-Band, a UC-Berkeley graduate student studying the Bay Area's geological past. "There are no coherent markers. Some things have gone up. Other pieces of the crust have gone down. It's like a jigsaw puzzle and some big dog gets a hold of some pieces and chews them up"

The pieces of geological history scientists now have indicate a very different Bay Area.

Fifteen to 20 million years ago, the Diablo and Livermore valleys were one huge basin. Weber-Band says. Hills existed where the San Francisco Bay is today some 12 million years ago. Geologists believe those hills are now in Sonoma County. Everything west of the Hayward fault is thought to have shifted northwards because of tectonic forces.

"There is probably that much slip on the Hayward Fault," says Davis Andersen, professor of geology at San Jose State University.

The range south of where Mount Diablo is now probably rose up 10 million years ago. The hills in Berkeley and Oakland are estimated to be about 5 to 6 million years old.

Mount Diablo Young

Mount Diablo emerged some 3.5 million years ago. In fact, the Blackhawk foothills and the hills around the Livermore Valley - part of the larger Diablo coastal range that includes Mount Hamilton - are older than Mount Diablo.

"Mount Diablo is a fairly new feature on the landscape" Anderson says. By contrast, rocks making up the Sierra Nevada are 100 million years old. San Francisco's lumpy terrain, on the other hand, didn't completely rise until 2 million years ago.

The ancient San Pablo bay, which existed between 7 and 13 million years ago, probably looked much like San Francisco Bay; and elongated body of water stretching from where the East Bay hills are now south through the Livermore Valley to Fremont, east into Central Contra Costa County and probably northeast beyond Vacaville.

A recent sedimentary discovery by Buising suggests a major river flowed into the San Pablo Bay - just like the Sacramento River feeds the San Francisco Bay. In the Oakland-Berkeley hills, she unearthed ancient sand grains that possibly came from the Sierra Nevada. "it's like a fingerprint. We can say something must have brought that material down."

Surrounding low-lying hills were over-turned as Mount Diablo pushed up to its present elevation of 3,849 feet. It's as though a subterranean bulldozer plowed the earth over. This pancake effect, flipping the bottom layer over has brought the region's oldest bones to the surface at the Blackhawk Quarry. There were no complete skeletons left behind, just a jumble of bird, reptile and animal fossils.

"We get a worm's perspective," Dunn says. "We see it from the bottom. It gives you some idea of some of the forces you're playing with here."

Hills Still Rising

The Bay Area has continually been reshaped like clay. Its high and low regions were created by tectonic action - causing dips in the land or valleys, and compression, resulting in the uplift of rock. Fault creep and earthquakes, which triggers movements measured in millimeters year after year, changed the face of the land.

Even today, hills and mountains are rising. The Diablo Valley is being shoved under Mount Diablo, causing an uplift of about 3 millimeters a year. "That's tremendously rapid uplift," Weber-Band says. "It's a tectonic wedge and the valley is riding on top of it."

The search for ancient fault activity has a practical side, too. Some faults break so infrequently no one knows about them until it's too late.

"Some faults slip every 1,000 years," Andersen says. "We have no idea they are there. The Northridge Fault was seismically quiet for hundreds of years."

That which strikes fear in the hearts of Californians also inspires awe.

Think of the lithosphere - Earth's crust and upper mantle - as a rug. It is compressed by this subsurface pressure, crumbling and folding up. "That's the Diablo mountain range 10 million years ago," Buising says.

"It was just pushed, squeezed up," she explains. "The California coastal range is still coming up. We're in the middle of the process. It all comes back to life on the plate boundary, life on the edge."

Indeed.

"It makes you feel very small," Buising muses. "But you are part of something big - something big, complex and wonderful."

printed by kind permission of the Contra Costa Times.