Archive for the ‘oakland geology walks’ Category

Lower Piedmont Park walk (#28)

10 August 2012

Walk number 28 in Charles Fleming’s Secret Stairs East Bay winds around the fine homes and hills of Piedmont along the valleys of Wildwood and Bushy Dell creeks. Here’s the route, shown on the Google Maps topo base.

walk 28 topo

The first and last part of the loop is in the watershed of Wildwood Creek while the rest is in the Bushy Dell Creek watershed. (They run down Lakeshore and Grand Avenues respectively, separated by Warfield ridge, and combine down at Lake Merritt where their names are sunk in bronze by the pergola.) Geologically, the walk covers the uppermost part of the big Pleistocene alluvial fan and the edge of the Franciscan bedrock block that underlies most of Piedmont.

geologic map

We start at the Lakeshore-Winsor split in the stream valley and make our way toward the divide. On Portsmouth Road the high ground of the bedrock zone stands out ahead.

At the far end is a steep climb to Wildwood Avenue, where we can look back across the stream valley to the ridge topped by Calmar Avenue, on the Oakland side of the city line.

Turning the other way, we look over the valley of Bushy Dell Creek. Once a large formal garden, this part of the valley was filled and leveled for its current use as a sports complex. It appears never to have been a quarry, unlike Dracena Park to the north or Davie Tennis Stadium to the south.

We turn upstream along the creek, where the land is relatively untouched. Just above this spot is the site of what was reputed as a sulfur spring.

The geologic setting doesn’t really give much support for the presence of a proper sulfur spring like the one in Walnut Creek, but after all this time the question is moot. Certainly I didn’t notice any odor. The grotto was very pleasant anyway, and there’s real bedrock all around. It’s mapped as Franciscan sandstone of the Novato Quarry terrane.

The route goes farther up and takes a loop past a pair of boulders.

Take a close look at these: they’re genuine Oakland-style blueschist, globs of old ocean crust that have been carried tens of kilometers down into the earth along a subduction zone, then spat back out, possibly more than once. (The details are at the bleeding edge of California geology.) The one boulder displays good color and mineralogy:

The other has some nice slickensides to show us.

Coming back downstream and past the baseball diamond, we pass the entrance to the football field. The view looks down the valley toward the lake and downtown.

Near here we can see more exposures of the sandstone bedrock, but soon afterward the route returns to the alluvial fan. The two substrates make subtly different topography, but that can be hard to see given the heavily landscaped landscape.

Palm Drive offers a picturesque farewell view of the Bushy Dell Creek valley.

Again we cross the divide between the two watersheds at Wildwood Avenue. The near valley is accentuated by glimpses of the higher hills.

I never get tired of this stuff.

Here’s the route in more detail.

route map

The upper Piedmont walk (#29)

19 March 2012

This hills-and-paths walk is number 29, “Upper Piedmont Park,” in Charles Fleming’s Secret Stairs East Bay. It’s short and steep and quite scenic. Here’s the street route:

The geology is entirely on sandstone and related rocks of the Novato Quarry terrane of the Franciscan complex, so the geologic map looks a little boring, but the topography is on there too.

The numbers on the street route correspond to the photos that follow. The starting point is the elaborate exedra of Piedmont Park. It evokes the atmosphere of Piedmont’s first business, a “sulphur springs” resort that once sat here above the little city of Oakland.

Go behind the exedra and find the stairway down into the shady valley of Brushy Dell Creek. We have great weather in Oakland, but if you ever need to escape the heat, come here.

Brushy Dell Creek runs through a steep little ravine that exposes some bedrock ledges in the streambed: enigmatic Franciscan metamudstone. There is no trace of anything you might call a sulfur spring. Who knows what it really was.

This set of stairs on the other side is lined with serpentinite boulders for a colorful effect. But serpentine rock is not local to this spot; that would appear in the Franciscan melange higher up in the Piedmont hills at the Oakland line, the purplish patch in the geologic map.

After this the walk goes up into the hills where the views are wide. The local swales and ridges are charming.

The stairways and paths were designed into the neighborhoods back when streetcar lines served them. A hundred years ago it was still a virtue not to rely on a motorcar for commuting—automobiles were for pleasure and travel, and walking was simply the way humans were built to get around.

There is not a lot of bedrock exposed on this route, which is a bit surprising. But the Franciscan sandstone doesn’t have the variety of rocks that the melange has. It was quarried rather than cherished. However, this spot along Scenic Avenue exposes some of the shale that accompanies the sandstone.

Soon enough you get to the last, longest set of stairs. Be sure to turn around now and then as you ascend, to take in the views.

At the top is a little saddle from which you can peek across the neighboring ravine known as Moraga Canyon and spot the high Oakland Hills beyond.

The long stairs down from this point have the mark of their maker, the longtime contractor Ransome Construction Company. At one time Ransome operated the big Leona Quarry; at another time they were in Emeryville. Today they’re in San Leandro and going strong.

The end of the walk takes you along Highland Avenue, which as far as I can tell is the longest level road in Piedmont.

This topographic accident was surely exploited by the town’s founders to connect Moraga Avenue, the oldest road in the area, to the spring resort. And the street imposed its axis on the surrounding roads to make up the town’s largest area of traditional square blocks and straight roadways, a little bit of “flats” in a hilly community.

Davie quarry

30 January 2012

Davie Tennis Stadium is a set of courts in a former quarry, administered by Oakland but situated within Piedmont. But what about the stone, you ask.

davie chert

I haven’t checked the whole place out, but the exposures near the entrance display this dark chert or siliceous metashale. The quarry exploited the Novato Quarry terrane of the Franciscan complex, a large pod of which underlies Piedmont and its immediate surroundings. The terrane is mostly sandstone, but some fine-grained rocks occur in it too.

I’ll be leading a walk to this and three other Oakland quarries for the Oakland Urban Paths organization on February 11. Watch the OUP site for details.

The Pill Hill/Fairmount ridge walk (#20)

29 December 2011

This hills-and-paths walk is number 20, “Broadway and Oak Glen Park,” in Charles Fleming’s Secret Stairs East Bay. This is not a bedrock walk, like the previous ones I’ve featured, but a landform walk. Let’s start this time with the topography.

walk 20 topo

This walk starts in the bayside flats, crosses two hills and two streams, and returns from the side of a third hill. The first hill is Pill Hill, and the second (Fairmount ridge is my name for it) and third are lobes of the Adams Point upland. These are parts of a larger structure that is central to Oakland’s character, an ancient Pleistocene alluvial fan. Here it is, marked “Qpaf” on the geologic map.

walk 20 geologic map

This walk takes in the leftmost edge of the fan, crossing two valleys of the Glen Echo Creek system which dissect the fan. The creek feeds the narrow west arm of Lake Merritt.

All right, here’s the route with the locations of the following photos.

walk 20 route

Here’s the view up Hawthorne Avenue to the edge of Pill Hill. The land west of the fan is a modern alluvial flat with almost no topography to it beyond subtle levees along the modern Temescal Creek and the notorious filled-in marsh that once underlay the ill-fated Cypress Structure in West Oakland. The Pleistocene fan has fairly abrupt edges like this all around it.

pill hill

As you go over Pill Hill and Summit Road on its spine, take a close look at the topography ahead of you. The near ridge is Fairmount ridge, made of Pleistocene alluvium, and the distant hills are Cretaceous and Tertiary sedimentary rocks. The eminence at the foot of the high hills is the older Franciscan block that underlies Piedmont and upper Rockridge.

pill hill view

The walk goes down into the valley of Glen Echo Creek. Brook Street is named for the Broadway branch of the creek, which is culverted under Mosswood Park and runs open to the sky in the backyards here. This shot is at the foot of 30th Street.

glen echo creek

If you go upstream a little ways you can spot the culvert where the two branches join.

glen echo creek

Next we climb the other side of the valley up a long flight of stairs, then turn right and follow the ridge top, along Fairmount Avenue, for a ways. A detour of stairways leads to Hamilton Place, at the toe of the ridge (the new Whole Foods place cut into that toe; unfortunately I never got a good look at the cut). From here we look across the next valley, which I might as well call Harrison valley.

harrison valley view

This valley has a well-developed profile, but apparently it never had a permanent creek. The Oakland watershed map shows only a culvert here. Anyway, we walk up the far side of this valley and return west on classic Perkins Way, where we can look back at the other two ridges.

perkins way

Back up on Fairmount ridge, we stroll up quiet Kempton Avenue, where this nice driveway wall of California mariposite lives.

mariposite

Soon enough we find ourselves again at the steep edge of Glen Echo Creek valley. If you limit yourself to walking, Oakland is really quite a rugged place.

kempton avenue stairs

At the bottom is a precious remnant of early Oakland’s streambeds, Glen Oak Park. An old concrete bridge crosses the stream, and if you have time to stroll up and downstream there are some fine buildings here too.

glen echo creek

I would be remiss not to mention that a little farther, at the foot of Piedmont Avenue, is a good sushi place, Drunken Fish.

The Albany Hill walk (#35)

13 November 2011

Here’s another stairs-and-paths walk from Charles Fleming’s Secret Stairs East Bay covering Albany Hill, the “little hill” for which the city of El Cerrito is named. I covered its geology last month for KQED Quest Science Blogs, so this post is more about the details of what you’ll see as you take walk 35. Here’s the route map starting from the El Cerrito Plaza BART station. In the book, the route starts at San Pablo and Washington, but I have an extra path that’s not in the book. The numbers represent the photos in this post.

walk 35 route

Next is the topography . . .

walk 35 topo

. . . and here’s the geology.

walk 35 geologic map

The geology’s pretty simple: the hill itself is typical Franciscan sandstone of the Novato Quarry terrane, surrounded by Quaternary sediment shed from the Berkeley Hills. Cerrito Creek runs past its north end, and Marin Creek’s drainage lies to its south. The divide between them is a low ridge of older alluvium where Solano Avenue runs. This accident of topography, making Solano a ridge route, is a subtle but important part of that street’s charm (like Park Boulevard in Oakland).

We start to hit bedrock around the first set of steps—duh! That’s what makes the hill so steep. This set of steps, Catherine’s Walk, is the worst.

stairs
steps

Now it’s worth looking around as you proceed. First come views west over the Bay. Click this one for a 1000-pixel version: in the Bay, left to right, are the Albany Bulb, Brooks Island, Point Isabel and Point Richmond; across the Bay are the Golden Gate, Marin Headlands, Angel Island, Tiburon Peninsula and Mount Tam, each and all worthy geological outings.

bay view

Once you enter Albany Hill Park the bedrock starts to emerge more. The real opportunity to inspect and sample it comes later, though.

bedrock

The trail winds up the crest of the hill through eucalyptus woods, for a special experience. The people who planted these didn’t have anyone’s pleasure in mind: they were dynamite-makers who needed a fast-growing screen to help muffle explosions. (The same thing happened up at Point Pinole.)

eucalyptus

Up here you start getting views to the east. The rocks in the Berkeley/Oakland Hills are much younger than where we stand: about 10 million years old as compared to the 80-ish million years of the Franciscan here.

berkeley hills

At the park’s north end we hit the top of Taft Avenue and take it down the east side of the hill. Don’t miss the view south. Behind the downtown Oakland skyline is Black Mountain, south of Palo Alto.

oakland

Along Taft is a long roadcut where you can poke and bang the bedrock to your heart’s content. Unfortunately it’s pretty featureless sandstone. It points to a geographic setting, long ago, when huge quantities of fresh sand were being generated and carried offshore to waiting basins, perhaps at the bottom of submarine canyons like today’s Monterey Canyon.

roadcut

Now if you scrap the last part of the route given in the book, and instead stroll north on Adams Street to its end, you’ll find a cute little path running along Cerrito Creek back to San Pablo.

creek path

Albany Hill and Cerrito Creek have a history of neglectful exploitation, but they have allies today in the Friends of Five Creeks.


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