A new kind of shoreline

5 March 2018

Rising sea level is a threat to the Bay area. Already, king tides are flooding the levees and seawalls built for the last century’s ocean. I touched upon this topic a few weeks ago with my proposed walk around Lake Merritt in 2100, assuming that the Bay will be a couple meters higher than today.

Yesterday, happenstance allowed me to witness a promising project that has built an experimental coastline modeled after a natural one — specifically, a living water filter meant to sit between the low tidal mudflats and the higher levees holding the Bay back. The Northern California Science Writers Association arranged for a group of members to visit the Horizontal Levee Project, on the grounds of the Oro Loma Sanitary District wastewater treatment plant in San Lorenzo.

Let me sketch the idea behind the project. To begin with, the natural coastal landscape has been totally messed up. It used to be a nice grassland plain, gradually sloping down to a series of wetlands that merged organically into the tidal marsh, mudflats and open Bay waters. Water from the hills percolated gently down the streams and through the ground, nourishing a lovely ecosystem full of species. American settlers cut off the top part of this landscape and covered it with buildings, dammed and diverted the streams, then filled in and walled off the lower part with levees. Today the coastal wetlands are cut off from the water and sediment from the hills, and meanwhile the sea is creeping up and washing them away.

The thinking behind the Horizontal Levee Project is to build a new slope on the uphill side of this truncated coast, then restore the groundwater flow that used to be there using treated wastewater. Even compressed to a fraction of its former width, the resulting slope should be a powerful water-scrubbing engine and a vibrant habitat. (Figure from here.)

The wastewater part is crucial because we have lots of it, we can control its flow, and the new slope — scientifically, an ecotone — cleanses the wastewater of nitrates and other hard-to-remove compounds better than treatments costing 10 times as much. All while feeding a splendid tidal marsh that resists storm waves better than concrete walls!

Our visit took place on a brisk, bright day by the bayshore. The Oro Loma Sanitary District treatment plant is mostly clean, stark and Brobdingnagian.

But the operators found space to put up this pilot project on their own land, where they didn’t need so many permits. They built a gently sloping earthwork, installed pipes at the top and drains at the bottom, then raised a mix of plants from local sources to seed it with, using these planter boxes.

Project staff noted that the alkali bulrush is particularly good at resisting storm waves with its tall, stiff stems.

Seeding and planting happened in the rainy season of 2015-16, so this lush jungle of native marsh plants on the ecotone was just two years old. It’s so dense that invasive weeds, even pampas grass, don’t stand a chance.

And the water coming out at the lower end is really clean. (Even so, the water was pumped out through the white pipes on the left and put back into the treatment stream.) Soil bacteria actually convert the nasty nitrate to nitrogen gas, so it isn’t just trapped in the dirt or building up within the plants.

Water treatment agencies all around the Bay have their eyes on this experiment. It looks like the design will be flexible enough to be adapted for as much as 5000 acres of wetlands, a significant fraction of the coastline that’s particularly vulnerable to sea rise.

Awareness of sea-level rise needs to happen faster than the rising sea itself. The speakers yesterday found that the hardest nut to crack in moving things forward is regulations: interpreting them creatively, coordinating the regulators, combating inertia. To envision, scope, design and plan improvements to the shoreline literally takes decades, meaning that we have to aim for a target in the year our children reach our age.


Redwood Ridge and the Parkridge land bridge

19 February 2018

Redwood Ridge is a name I made up to keep things straight. Let’s start with the part of the USGS topo map showing the south end of Oakland’s redwood country. Redwood Ridge is just east of Skyline Ridge (another name I made up), which starts where Joaquin Miller Road meets Skyline and extends to Lake Chabot.

Oakland was a redwood lumbering town before it was anything else, and the great redwood groves gave their name to features all over the hills. Redwood Peak sits at the top of the map, and east of it is Redwood Creek running down a straight valley that leads to Upper San Leandro Reservoir. That valley has no formal name, so I dub it Redwood Valley, the valley of Redwood Creek.

A major tributary of Redwood Creek flows out of a steep-walled valley named Redwood Canyon, clearly marked on the topo map starting with the 1947 edition. So, Redwood Canyon cuts through Redwood Ridge and ends in Redwood Valley at the point where Redwood Road meets Redwood Creek. Got all that? Good, because I won’t repeat it.

From here on out I’ll show maps that have been tilted for easier viewing. Here’s Redwood Ridge in the handy terrain view of Google Maps.

This post is about the south part of Redwood Ridge. It’s a pretty cool piece of land, just to look at on the map.

The top side is bounded by Redwood Valley and the left side is defined by the lower part of Redwood Canyon, a classic water gap. Now look at the bottom side. On the right is Grass Valley, with Grass Valley Creek flowing through it down to Lake Chabot. On the left is a smaller valley that lines up with the upper part of Redwood Canyon. It has an unnamed stream in it. I’ll call it MacDonald Creek, because that’s the name of the trail there.

The last thing to notice is that little land bridge leading from the end of Parkridge Drive, right where the valleys of MacDonald and Grass Valley Creeks meet. The two creeks have been eroding their way toward each other. They seem to be evenly matched, but I think Grass Valley Creek may have a slight edge. The photo portion of this post starts there.

But first, the bedrock map. It shows that those two creeks have been exploiting the softer rock of the Shephard Creek Formation (Ksc), sandwiched between the Oakland Conglomerate (Ko) holding up Skyline Ridge and the Redwood Canyon Formation (Kr) holding up Redwood Ridge. Rare are the places where Oakland’s bedrock is expressed so clearly on the landscape.

And here’s the park map with the details on the trails.

As you descend Parkridge Drive to the trailhead, Redwood Ridge appears as an island of forest.

In my three visits here, dog walkers made up the great majority of people using the park. (Be sure you or your walker supports the park by carrying a permit and following the rules.)

Starting out across the bridge feels magical.

And at the right time of day as if by magic, the bedding planes of the Shephard Creek Formation appear out of nowhere. The geologic map indicates that these beds are overturned.

The view from the bridge extends to the right down Grass Valley toward distant Fremont Peak.

And to the left, the view from front to back encompasses MacDonald Creek valley, Redwood Canyon, the massif of Redwood Peak and Round Top beyond with its bare southern shoulder. Redwood Canyon still grows a few redwoods, but in the mid-1800s they must have filled the canyon to the brim.

The MacDonald Trail is excellent for all users, including horses and (since 2016) bikes. The woods are enchanting in any weather, but they photograph best on shady days.

So does the bedrock in the road. The Redwood Canyon Formation is primarily fine- to medium-grained sandstone that shows the marks acquired over 80 million years of geologic history. It’s soft enough to be graded without blasting. The ridge stands as high as it does not because the rock is especially hard, but because it absorbs water so well, inhibiting the surface runoff that so effectively erodes the stream valleys all around it.

Off the road, the sandstone occasionally crops out in bulbous boulders. When Jim Case mapped these rocks for his PhD thesis in the early 1960s, he described these as “cannonball concretions,” but from my observations so far I think he was mistaken, and the description of this unit on the geologic map (circa 2000) does not mention them either. I think this is ordinary weathering like you see in arid and semiarid country all over the West.

The previous three photos are from the north side of the trail. The south side offers wider views of Grass Valley and beyond to Loma Prieta and the Sierra Azul west of San Jose at far right.

And you must not miss the stub of Brittleleaf Trail, which leads to a sandstone spur overlooking lower Redwood Valley. Surrounded by blooming manzanita at this time of year, the tranquil spot hums with bees and invites a long sit. Naturally I inspected the sandstone and determined to my satisfaction that its beds are overturned and dip steeply at 75 degrees. Notice that the fractures in the sandstone have no relationship to the original bedding.

The view south from here looks over the reservoir and watershed lands, the bare green ridge known as The Knife west of San Ramon, and the Diablo Range mountains south of Livermore against the horizon.

The view north, from far to near, includes the Briones Hills, tower-topped Mulholland Hill in Orinda and Moraga, the south end of grassy Gudde Ridge with its water gap where Canyon Road cuts through, a bit of wooded Canyon Ridge, and chaparral-covered Pinehurst Ridge, the type area of the Pinehurst Shale. All are worthy destinations of their own.

This is the best time of year to see these lands. Among other reasons, the poison oak has begun to sprout, making it easily visible, but not yet spread over the woods and side trails, keeping you out.

Care and grooming of rocks and outcrops

5 February 2018

Photographers know that everything about a great shot depends on how you set it up. As I capture images of geological subjects, part of the setup involves prepping the model. Often it’s just a matter of removing a few stray twigs to get a decent picture, like these serpentine stream cobbles in Joaquin Miller Park.

Only rarely does nature present rocks in an untouchably satisfying way — and to tell the truth I might have brushed off a cobweb before I took this portrait of laminated siltstone in Shepherd Canyon.

But around here, as opposed to the Grand Canyon, rock exposures are generally kinda shabby. What are you going to do? Rocks are made underground, and once exposed to surface conditions they start to break down. And vegetation doesn’t care where it sheds things.

In many of my outings, I find myself doing some housecleaning. Whenever I lead a walk, it’s mandatory for me to go over the route beforehand and groom the features I plan to show off, like the splendid exposures of the Oakland Conglomerate in Montclair.

This textbook example of load casts always requires a thorough weeding session, followed by a good sweep with my umpire’s brush. Because shale wants nothing more than to return to clay, and weeds like nothing more than decayed shale.

There’s an outcrop in Dimond Canyon, along the trail, that I always take a minute to groom. The last time I did this I took these before-and-after shots.

This is something that any of you can do too, if the spirit moves you. I know people who routinely carry tools to prune snaggy or undesirable vegetation along the trail in a discreet way. Sometimes I do that, but more often I stick to grooming the outcrops. Because who else will? While one of my principles is to “leave the stone alone,” the stone can use a bit of care here and there. That’s my contribution to the geoparks movement in a country that badly needs it.


Tour of the Fan: Lobe 3

22 January 2018

This post takes a look at lobe 3 of the Fan. To orient you as we start, here’s where lobe 3 fits in the bigger picture on the geologic map.

This is the best time of year to walk around the Fan, in the Oakland midlands. When the trees are bare you can see farther and better — the landscape’s bones stand out, and the homes do too. So get yourself on out!

This lobe is more difficult to explore than the others. One problem is that the trees are larger and the landscaping thicker, which makes it hard to get a good view around you. Another is that the streets are laid out in a distributary fashion — that is, you aren’t expected to drive through it except in a couple of places. You’re supposed to drive into it, to your single-family home or small apartment building, and out of it, to work or shop. So getting around in any other direction is not straightforward.

Maybe this will be clearer on the geologic map. For convenience, I’ve divided the lobe into four sublobes.

I tend to analyze landforms from their ridgetops and divides and saddles, features on top of the land. But lobe 3 may be easier to comprehend as a set of stream valleys dissecting a highland, as shown in this watershed map from the county flood control district.

As with the other parts of the Fan, the edges of lobe 3 are pretty clear-cut. This is typical of eroded landscapes in arid country, which is interesting because Oakland isn’t especially arid these days. It was during glacial times, though. Here’s the north edge at the south end of Ramona Avenue, just west of Mountain View Cemetery in the valley of Glen Echo Creek.

This view across the Glen Echo Creek valley up Monte Vista Avenue gives a better idea of the height of this lobe — about 80 feet here, but it seems like much more.

At its westernmost edge, the lobe starts right where the Whole Foods store stands. Everything in front of the far hills is part of the Fan.

This shot from the toe of the Calmar sublobe shows why the Fan has always been land to make homebuilders salivate: fantastic views of the city, the Bay and the Golden Gate. Adams Point fills the middle ground.

And here’s a final view across the edge of the lobe, this time as seen from the freeway overpass over the homes in Trestle Glen. Longridge Road along the top gives its name to this sublobe.

The Adams Point sublobe is larger, but a little lower than the others, reaching about 160 feet elevation. Its highest ridge, along Fairmount, Kingston and Rose Streets, offers good views north toward lobe 2.

Points on the other side, like Jean Street and the knob of Nace Avenue, overlook nice vistas south and east. Or Cambridge Avenue.

The Warfield sublobe is a highlight of geology ramble 4. Whereas the Adams Point sublobe has saddles where three roads cross it (Santa Clara, Linda and Grand Avenues), you have to hump Warfield Ridge over Mandana Boulevard, as here:

or go up the Bushy Dell Creek valley on Wildwood Avenue and over to Winsor Avenue. In between it’s a bit intimidating, as seen from the foot of Jean Street.

The Calmar and Longridge sublobes are the highest, reaching well over 200 feet elevation at their upper ends. Longridge is particularly hard on landscape photographers because there are so many mature trees and big homes. (If only it were 100 years ago, when this whole tract was bare hills.) But I like this shot from Long Ridge. On the right edge it shows the red-brick Grandview Apartments building (Warfield sublobe), the Spanish Revival apartment complex on Crescent Street (Adams Point sublobe), and behind them the big palm tree at the top of MacArthur by the Chetwood overcrossing. A little bit of Elwood Street is visible to their left.

But if finding big views is frustrating, it’s easy to find cute little pocket valleys all over lobe 3. The only one I’ll point to here is the one with the Morcom Rose Garden in it.

Here’s where all twelve photos were taken.