Infineon Raceway, previous known as Sears Point sits right on top of the Tolay Fault. Despite my poking around from time to time I didn't realize that until this morning. In one of the photos at the attached link you can see a hill which I drove by one morning on a detour to work which truly looks like an extinct volcano.

Today's Press Democrat on-line news delivered a story about a regional park which will sit right on top of the Tolay Fault. I think everyone should have a park on a fault. In addition to the article, I've also selected some text about the geological make-up of the fault and lastly, there is a link to a marvelous field trip taken a few years ago with terrific photos which will bring you and this story, so much closer together.....Enjoy....Petra

Site of planned Tolay Park rich in history
Sunday, November 7, 2004

By GAYE LeBARON
THE PRESS DEMOCRAT

It's the classic early California scenario: the brown-robed friar riding his donkey into the wilderness, looking for a place to build his mission.

In some stories, he leaves a trail of mustard seed behind him that blossoms into a wide golden swath in the springtime. In others he meets grizzly bears or finds beautiful Indian maidens who beg to be baptized.

In this story, the friar finds a lake. Not Tahoe, not even Clear Lake. Not that big. But a lake nonetheless, worth writing about in his diary: "We found, on said hillock, a little farther on, the large lake of Tolay."

It's been more than 180 years since the Rev. Jose Altimira, the Franciscan friar in charge of Mission Dolores, or as it was properly known, Mission San Francisco de Assisi, was rowed across San Francisco Bay accompanied by 20 soldiers from the Presidio and led an expedition into the hills along San Pablo Bay.

There he found the sizable freshwater lake which, according to the Indians who were camped there, was called Tolay - named, they told him, for a former chief of the Indians who populated the area.

Padre Altimira was looking for a place to build a mission, and it's possible that he considered the lakeside site. The lake, he estimated, covered about one quarter of a league, or 1,100 acres. And while the water was sweet, the lake was filled with tules and he was afraid it would not be a sufficient water supply for a settlement.

So he led his party, which included a deputado from the Mexican government, to the east, where they found forests of oak trees, handy for making carretas, those two-wheeled carts favored by Californios for transportation, and a creek, which the Indians called Sonoma, with an abundance of fresh water.

That's where Altimira decided that the mission, named for the other St. Francis, San Francisco Solano, would be built, and where the pueblo of Sonoma was established a decade later.

When Mariano Vallejo was sent from the Presidio to govern Mexico's Frontera del Norte, the described boundaries of his 66,600-acre Petaluma Rancho included Lake Tolay.

One of them was a German immigrant named William Bihler who bought that portion of Vallejo's rancho. Not satisfied with the number of potatoes and corn stalks the land around the lake produced, Bihler joined the many early Californians who took nature into their own hands.

Bihler is described by historian Robert Thompson in the first Sonoma County history as "a utilitarian." Today's environmentalists would choose a different name. He dynamited the southern end of Lake Tolay and watched with satisfaction, one supposes, as the water drained out into the bay, down what became known as "Bihler's Slough," leaving behind 1,100 more acres of extremely fertile land.

The lake, wrote Thompson in 1877, "is now a potato patch."

NOW, 145 YEARS later, there are Californians of a different persuasion who are lining up for the privilege of sticking a big toe into a restored Lake Tolay.

We don't often get a chance to re-create history. And you know we're not going to build a better mission or make the land grants smaller. But, with Mother Nature and the open space district on our side, Sonoma County is going to bring back Lake Tolay.

AND SUCH a place it is! The valley nestled between two mountain ridges makes it one of those properties where you can see forever - Mount St. Helena, Mount Diablo, Mount Tamalpais, on a clear day, the Golden Gate Bridge.

It's where tens of thousands of wild ducks and geese stop in on their annual migrations, where golden eagles soar.

SO, WHAT, EXACTLY, will there be in Tolay Park?

That's a question that neither Sales nor Cardoza can answer just yet. The plan is being designed. The drive to raise the remainder of the funds is under way. Rene Tolliver, who was with United Way here, was hired last month as campaign manager.

But if you take the "exactly" out of that question and just imagine, you can see them coming up the hill from Lakeville Highway: The hikers and joggers and mountainbikers and horsemen, the bug chasers and bird watchers, the picnickers and the city dwellers seeking a breath of fresh air, and, yes, the kayakers and canoeists, coming for a day's paddle on Lake Tolay.

http://www1.pressdemocrat.com/apps/pbcs.dll/article?AID=/20041107/NEWS/411070335/1067/NEWS06

Beginning in the early part of the Pliocene Epoch, a volcanic sequence was deposited in the south-central part of the county. After a subsequent period of erosion, deposition began anew, forming the sediments which now constitute the Petaluma Formation. The depositional environment of the Petaluma Formation consisted of shallow to brackish water embayments which had been eroded into the landscape formed from the Jura-Cretaceous and later rocks. Following deposition of the Petaluma beds, a period of orogeny occurred, which tilted, folded, and uplifted these beds while still young. This caused a widespread period of vigorous erosion, during which much of the then-soft Petaluma sediments were stripped off. By that time, much of eastern Sonoma County was above sea level, and here and there were lakes filled with water, which supported large communities of diatoms. At about this same time, movement began along the Tolay Fault, which caused a displacement of several thousand feet of formerly adjacent sediments.

http://www.sonoma.edu/users/n/norwick/Document/Ford/gwsappd.html

The attached link displays photos of the entire region taken on a field trip. Don and I met Carolyn "Carrie" Randolph at the AGU two years ago when she presented a poster. Rolf Erickson is a Professor at SSU who I met a few years ago over coffee.

• Field Trip Excerpt with Photos