Introducing Deep Oakland 6: The Fan or Second Level

26 September 2022

Chapter 6, the central one of the eleven in Deep Oakland, is about a feature I would bet most Oaklanders have never given a name: the distinct arc of low foothills above Foothill Boulevard and around the head of Lake Merritt. Its hills are so hidden by homes and trees these days that my favorite photo of them is this old one from 1876, looking across Lake Merritt from 12th and Webster.

Of course, my regular blog readers have seen me write about this arc for years under the name of the Fan. It’s an intriguing set of old gravel hills that lies above Oakland’s first level (the shore and flats) and below the third level (the bedrock hills of the Piedmont block and the Millsmont-Eastmont hills), the fourth level being the high Oakland Hills east of the Hayward fault.

The simplest way to illustrate the Fan is to show it on the bare topography (digital elevation model) of Oakland with the geologic map of the same area next to it:

I call these hills the Fan because their crescent shape on the map reminds me of a tattered Japanese folded paper fan. They’re shown in a darker yellow than the flats, signifying gravel and sand and clay that’s coarser, older and more consolidated than the alluvium around them.

This ragged swath of large sediment piles presents a geological puzzle. My solution to the puzzle of the second level combines all the stories of Oakland’s geology I’ve told so far.

I’ll come back to the geology in a bit. First, some history.

In the old days the Fan was just another part of the Ohlones’ rich world; they kept it mostly tree-free with regular mild fires and harvested in season the plants and small game it supported. But it stymied the first explorers from New Spain in the early 1770s, who tried to walk around it along the Bay side. The trouble was, that route dead-ended at the slough we know today as Lake Merritt, and they had to detour past the marsh through those hills which, as Friar Pedro Font recorded in 1772, “annoyed us very much with their ascents and descents.” Four years later the Anza expedition found and took the correct Ohlone trail, the same basic route that I-580 takes today. The NL and 57 bus lines are good ways to survey the Fan in comfort.

The first Europeans to settle in Oakland territory, the Peralta family, picked a spot in the Fan for their first hacienda, and ever since it’s been a desirable place to live. To the Peraltas it was good pasture, to the Americans that followed it was good land for farms and country estates, noted for its “picturesque scenery on every side,” and in the early 1900s it became Oakland’s most desirable streetcar suburbs.

I love taking long walks in the Fan’s charming ups and downs, although the deeply dissected hills around Lake Merritt (Adams Point, Grand Lake, Cleveland Heights) are more challenging than the rest.

One thing that’s significant for me as a geologist is that the Fan wraps around the Piedmont block, which is the chunk of blue colors on the geologic map representing bedrock. I can safely assume that both the block and the Fan that embraces it were uplifted together. And what did that?

As I said in chapter 1, the Hayward fault is Oakland’s prime mover. It’s been carrying this part of town north for millions of years. And if you run the fault backward in your mind, about a million years ago the Piedmont block was down by San Leandro, where the fault was forcing it past the big body of solid rock that makes up the hills there. When the irresistible force of a fault does this, the immovable objects it brings together have nowhere to go but up, and that’s what I think happened: the Piedmont block got hip-checked. As further evidence, I cite the odd presence of deep Dimond Canyon cutting through the Piedmont block.

It makes sense if powerful San Leandro Creek was flowing over the block while it was rising, carving this textbook water gap. That hypothesis — a mix of inference, deduction and corroboration — is my contribution to science. I feel pretty confident about it.

Introducing Deep Oakland 5: The Piedmont Block

19 September 2022

Oakland is unusual in having Piedmont, an independent city, entirely inside its boundaries. Geology accounts for that. Little Piedmont got its start with resources from the little range of hills it sits on: water, soil, stone and prime residential land. Chapter 5 of Deep Oakland is about that set of rocky hills, the same hills that Mountain View Cemetery sits on. It’s the forested ridge in this view from the north side of Claremont Canyon.

The hills are the top of an uplifted block of the Earth’s crust in an unusual place: the west side of the Hayward fault, where almost everywhere else the west side is being gradually pushed down and buried. The rocks in it belong to the Franciscan Complex, which I introduced in chapter 4. The upper part of it is melange, which is apparent as one crosses the fault from Montclair to enter the block:

The landscape in the Piedmont block feels different from the high hills east of the fault with their roller-coaster roads and steep, straight flanks; the slopes here are gentler and more rounded. What’s different is the Franciscan bedrock underfoot.

This chapter, like some of the others, traces a route and has a direction. It leads from the pass at the top of La Salle Avenue down the full length of Blair Avenue and ends at the lower edge of the Piedmont block at Broadway and Pleasant Valley Boulevard, former site of a rock quarry. Along the way the melange gives way to hard sandstone, “rock that was once worth money.”

Blair Avenue is named for Piedmont’s first American landowner, Walter Blair, a farmer from Vermont who bought property in these hills and started a dairy farm and a rock quarry to serve the young town of Oakland below. The profits helped launch Blair’s other projects: a resort centered on the mineral springs of Bushy Dell Creek, a family-oriented nature fantasy park, selling residential lots to wealthy white people and operating a streetcar line to and from Oakland to serve Blair’s realm.

The mineral springs are now remembered in old photos and in reconstructions with interpretive signage.

The bedrock on Blair’s land was the nearest source of stone for Oakland builders, thanks to its odd position west of the Hayward fault. And Blair cashed in when the city began a major infrastructure project: paving the sandy streets of downtown Oakland with crushed stone by the macadam method. Other quarries soon started up, and after a few years two of them, the Oakland Paving Company and the Alameda Macadamizing Company, teamed up in a competition-quashing duopoly that lasted until asphalt and concrete paving succeeded macadam, around 1900.

By then the pattern that Blair began was set: wealthy residences covered the desirable hills as the quarries began to fade. The residents of Piedmont voted to incorporate in 1907, two years before Oakland annexed everything around the new city and made it an enclave. Just as Oakland had begun as a genteel refuge from raucous San Francisco, so Piedmont became a place apart from the booming city around it, as did the ring of Oakland land that adjoins it.

The quarries closed, but the old pits couldn’t hide. Today they offer access to the same rocks that compose Mountain View Cemetery’s hallowed ground.

I love quarries, the way geologists do, as scalpel incisions that expose the underworld in detail. I’m grateful for their old, slowly healing scars. The quarry stone from the Piedmont block was well suited for building roads and foundations: hard, durable and consistent. It could be predictably crushed into clean stock and sorted easily into different size grades. One could make steady money with it by keeping costs low.

There have been at least six rock quarries in the Piedmont block. The two that most people see are the one holding Zion Lutheran Church on Park Boulevard . . .

and the one holding the Rockridge Shopping Center, which for much of its eighty-odd years was the largest quarry in Alameda County.

What does the Piedmont block mean to the larger landscape around it? Its location near the Bay, on the west side of the Hayward fault, means that it collects rainfall in a broad, unified catchment. For the last million years or so, every time there’s a great rainstorm the five permanent streams on the block feed that water toward the Bay in a strong, coordinated flush. If you recall from chapter 2 that most of the time, geologically speaking, the Bay is a dry plain, you’ll see why those streams keep digging a deep ravine where Lake Merritt sits.

The two odd landforms, Lake Merritt and the hills of Piedmont, are related. Okay, thinks the geologist, now what accounts for the Piedmont block? I present more clues and a hypothesis in the next chapter.

Introducing Deep Oakland 4: Mountain View Cemetery

12 September 2022

Chapter 4 of Deep Oakland is kind of a curveball that I quite enjoyed researching, pondering and writing. The magnificent Mountain View Cemetery, founded in 1863, was designed to suit the special landscape, and the geology that it happily preserved shines through to this day. It embodies an important element in Oakland’s geology. But here too are some graves of notable geologists — and geology is people. In this chapter, which is formally about perceiving landscape, I touch on a range of human topics: the nature of science, the nature of wildness, the minds of geologists and the role of geology and geologists in human society. Those are things I don’t blog about, so I think my regular readers will enjoy this chapter. The ideas in it underlie everything I post.

Here are no ice-age scenarios; instead, my ruminations sift through centuries of human time, starting in the early 1600s with the birth of modern science. However, in this chapter I also bring up rocks for the first time and try to explain why geologists care so much about them:

Asking a geologist “what are rocks?” is like asking a chef what food is, or a writer what words are. They will smile, pause and answer, “The real question is what rocks mean.” Rocks are more than lumps of mineral matter. Rocks are things that have happened, results of particular events. Every body of rock was made in a specific place and time, and it’s stamped with traces of that environment as surely as a serial number, if we have the skills to read it — that belief is what drives geologists.

The rock that underlies the cemetery is rarely visible unless you see a few chips around a fresh-dug grave: it’s thin-bedded shale and sandstone, not too hard to dig in and good for growing grass and big ornamental trees, but it doesn’t crop out. Within it, though, are lumps of very different stuff, like raisins in a pudding, and they punctuate the landscape at all levels.

This mixture, blocks in matrix, is called melange and it’s found all over the Coast Range as a major part of the Franciscan Complex. The Franciscan pops up later in the book, so that’s all I say about its rocks in this chapter. But melange makes a peculiar, casual terrain well known to California geologists: “Seeing melange here outside its main habitat, groomed and ornamented with trees, can bemuse geologists who know it from genuinely wild places.”

I talk about geologists in the cemetery, some of them famous and others revered only by specialists. The foremost of them, Joseph Le Conte, is also the most problematic: “Every age reconsiders its heroes once they fade from living memory, and lately he has been found wanting.” Considering his legacy, good and bad, leads me afield as I walk around the grounds. I also harken back to Francis Bacon, who invented modern science in Shakespeare’s time, and Nicolaus Steno, who a few decades later founded geology (and is literally its patron saint), and his three degrees of beauty. I hope more of my readers will check out these thinkers some time.

I also ponder the ideas of landscape and wildness, and Le Conte, a founder of the Sierra Club, turns up again. He loved the grand empty lands of the Sierra Nevada and thought they were better off without the Indians who formerly called them home. Geologists have a certain possessiveness about the land, a willingness to cross fences, that needs careful taming. I’m as susceptible to it as anyone.

In sum, the geologist’s eye is a bit subversive; it ignores boundaries and other restrictions, legal or sacred. With equal curiosity we scrutinize the stones of churches, the floors of civic buildings and the walls of lavatories. And so it is with me and this cemetery. It’s a handy example of what California geologists, with easy familiarity, call Franciscan terrain.

If you feel like visiting Mountain View, be aware that they’ve restricted their hours since the pandemic began.

Introducing Deep Oakland 3: Downtown

5 September 2022

Deep Oakland starts in chapter 1 with the tectonic Earth forces, embodied in the Hayward fault, that have constructed our city’s landscape; chapter 2 adds to it the cosmic cycle of ice ages that have played out their changes on Lake Merritt, Oakland’s unique water feature. Chapter 3 adds a third thread to the braid that runs through the rest of the book — the imperatives of city-builders and how they react to the local geology, both the opportunities presented and the limitations imposed. Here’s where we get into Oakland’s human history.

Oakland was founded by a trio of scoundrels: well-connected lawyers, led by Horace Carpentier, who grasped the potential of this site and set out to build a prosperous city on its open stage:

This wooded plain by the Bay, they could tell, had the bones of a proper city. And there was something special about it, something beautiful. Though they could see the country differed from the rest of the East Bay, they couldn’t tell how natural forces had made it that way.

They saw that unlike the shores elsewhere in the East Bay, which were either forbidding rocky slopes or soft marsh, here was a platform with the makings of a good harbor. Ships could reach it, with care, through a sheltered inlet and drop anchor by the sandy bluff along its southern edge, a setting made for wharves and piers. Unlike rough-and-tumble San Francisco across the Bay, it was land free of cold Pacific fog, unstable government and unruly culture, where streets could be laid and lots offered to homebuilders in an orderly way. Everywhere, mature trees provided ready-made shade for elegant estates. They saw land ripe for processing and sale.

The sandy platform bore an encinal — a forest of evergreen oaks — that had suffered neglect in the sixty years since the Spanish removed the Ohlones from their land.

The conspirators staked out large claims on this land, then wrested it from its owners by wearing them down in court. They hired a surveyor to lay out a perfectly rectangular grid of streets that happened to feature amenities we still enjoy today: views of significant mountain peaks in all four directions. Then they organized a government to exert power in their personal interest.

The oaks were mostly gone within thirty years, cut down for firewood and charcoal. (This was not our first timber rush: the redwood rush had started a decade earlier.) Carpentier couldn’t save them, though he tried, calling the oaks “the chief ornament and attraction of this city” in his first mayoral address and even naming the new town after them.

He had in mind a genteel suburban town of tracts like Pardee House, the last bit of Carpentier’s vision left within Oakland’s original street grid.

There were other resources in the sandy platform, geological ones. First was the virgin soil, which was fantastically fertile. Second, wells could tap good water everywhere, no more than sixty feet down. Soon both of these were exhausted, the soil by overuse and the water by overpumping and pollution. But for a while, excellent estates were possible, graced by the instant elegance of mature oaks.

And then the city moved on, dismantling the estate lots for development and exploiting water and soil elsewhere in its neighborhood. I revisit these resources in later chapters. But the sandy platform still had more to offer.

I mentioned last week that the fine sand of downtown Oakland is related to the great field of sand dunes that covers San Francisco beneath its urban cover. The dunes came into being during the latest ice age as the ocean dropped by some 400 feet, exposing the sandy seafloor all the way past the Farallons. Ice age gales, more intense than today’s sea winds, brought the finest sand back ashore and built up a blanket some sixty feet thick. Our outpost, which extends beneath West Oakland too, is mapped as the Merritt Sand.

This ancient windblown sand, mixed with a little ancient windblown clay, is about as good a foundation material as there is short of bedrock, and easy to work with. Look for it in any excavation.

It’s beautiful material, dense and firm, the color of caramel, without a single pebble in it.

We’re lucky to have this good foundation material, because bedrock is out of reach in the East Bay flats, buried by hundreds of meters of sediment. Downtown Oakland has grown upon this base into a new encinal of concrete, stone, tile and steel, with a new generation of towers clad in glass that suit this young century in the ways they play with mass and light.

I spend a good part of this chapter celebrating the use of stone in downtown’s buildings, and I point out some favorites that long-time readers may recognize.

You can appreciate this terrain today in several ways. All the streets heading south from West Grand Avenue (more precisely, 20th Street) climb up the edge of the Merritt Sand. The big West Oakland parks — Raimondi, De Fremery, Lowell — all display its impressive flatness and wide views. Snow Park sits on its edge. The bluffs along Lake Merritt show its topography; given that Andrew Lawson of UC Berkeley named it “from its occurrence on Lake Merritt, in the city of Oakland,” this is its type locality.

I sum up: “Most cities owe their germination to an accident of geology; Oakland happened to sprout on a field of sand dunes, its youngest landform. Deep time goes much farther back in Oakland’s other places. Keeping the preliminaries I’ve laid out in mind — the forces of the fault, the cycles of the sea and the impulses of city-builders — let’s pay them a visit.”