Merritt Slough

When Oakland was first settled, a large wetland extended inland from the tidal channels east of Alameda Island. Samuel Merritt took it upon himself to improve the marsh with a dam, and the resulting brackish water body was named Lake Merritt. Today the lake is closely regulated with a water gate beneath 7th Street, and this creek runs both ways depending on the tide. Not even the Oakland watershed map gives this stream a name, so I’ll call it Merritt Slough. Click the photo for a 800×700 version.

The bank on the right side is the south bank, or the left bank. It’s nearly in its natural state, whereas the other bank is part of an area of made land a couple hundred meters wide. I’m standing just off E. 10th Street, next to the Civic Auditorium.

Two dams

I was asked the other day about the safety of living below Oakland’s dams. We have two of them, both of which I happened to photograph in March 2003 (back when I was still using film). Anthony Chabot built them both. This is the dam at Chabot Reservoir, at the very south end of Oakland. The Hayward fault is a couple hundred meters downstream.

This is the dam at Lake Temescal.

Both are earthen dams, basically massive piles of clay and boulders. The first was built in 1874-75 and the second in 1868. As the “great San Francisco earthquake” occurred on the Hayward fault in 1868, seismic safety was high in people’s minds. Here’s a page about their construction. These dams are generally considered sound and able to withstand another big one. Lake Temescal straddles the Hayward fault, but the dam is so massive and the water it holds so modest that even a 2-meter displacement on the fault will not lead to a dangerous failure, as I understand it.

The Calaveras Dam, farther south near Milpitas, is also of earthen construction. It crosses the Calaveras fault and is being replaced with a safer design; in the meantime the Calaveras Reservoir has been drained to half its volume.

Quarry pond fixed

For several months, the quarry pond at the Rockridge Shopping Center at Broadway and Pleasant Valley was mostly drained while a crew built a new drainage system. The water grew very clear over the summer, but I never managed to get back to the cliff overlooking it to see what was visible. Too bad—the work is done and the pond is full again, its bottom probably never to be seen in my lifetime. This habitat must be pretty sterile at the moment, but the geese sound happy to be there. The creek has been noisy, too.

Vantage Point Park

This tiny park is at East 12th Street and 13th Avenue, on a low rise next to a lot of activity. Between here and the water—Brooklyn Basin, the innermost part of Oakland Inner Harbor—run East 8th Street, I-880, Embarcadero Street, BART and the Southern Pacific rail line, plus I’m sure a number of underground power and water lines and what not. It’s a highly concentrated lifeline corridor. Across the way is the Coast Guard base on Government Island. In the distant left corner in the 800×600 version (click the image) you can just see Alameda Island. Except for the hummock in the foreground, everything visible is made land, artificial fill, with a high water table. It was created more or less haphazardly starting a century ago, and under strong shaking a lot of old fill of this type is prone to liquefaction.

Past the left edge of this photo, a little buried creek valley running down 14th Avenue reaches the bay. It’s all filled in, too. All the crowded life lines I mentioned cross that creek bed. In the next big Hayward fault earthquake, this is a highly vulnerable spot.

I took this shot on 19 November 2008 during a walk I took the length of Oakland, from the San Leandro to the Ashby BART stations. Lots more photos from that day on my Fotothing site.

Sulfur mine creek

Lion Creek drains Laundry Canyon in the Leona Heights and Crestmont neigborhoods as well as the former Leona Quarry lands. It runs through Mills College, past Evergreen Cemetery, and into the bay at 66th Avenue — it’s the stagnant creek you see from BART just north of the Coliseum.

This is one strand of its headwaters, coming out of a former pyrite mine at the end of McDonell Avenue. The local chapter of the Society for Industrial Archeology says about this mine, the Leona Heights mine, “From the 1890’s to the mid 1930’s, iron pyrite was mined here and at the nearby Alma mine. It was processed into sulfuric acid at the Stege Works of Stauffer Chemical in Richmond (and other sites).” The photo was taken in 2003; I think it’s a little better today. The orange is iron oxides, not especially poisonous, but it looks awful. As I imperfectly understand it, sulfuric acid in the drainage water drops this mineral as it is neutralized. The acid comes from sulfur-eating bacteria in the mine environment.

Yes, Oakland has its own example of the same acid mine drainage that plagues the Appalachian states and many other lands. Every place the pioneers came to, they began mining everything they could, because that was the only way to build civilization. Sulfur is essential for gunpowder, and pyrite was the readiest source. Coal came from the Contra Costa hills, mercury from San Jose and from points north, lime from the San Mateo coast (and the local shellmounds), rock of all kinds from the Oakland Hills. This place was rich in timber and pasturage, we all know, but rich in minerals too.

Managing the lake

Lake Merritt needs a lot of care and attention to perform at its top level. This view of the pergola at its east end shows one of at least three aeration fountains in the lake. Without the oxygenation provided by these fountains, the organic matter brought in by the tides and streams, and deposited by the abundant bird population, would periodically overwhelm the natural oxygen dissolved in the water and turn the lake into a stinking anaerobic pond.

Without upkeep, this site would quickly revert to the tidal marshland that it once was. That would be nice in its way, but city-dwellers would probably complain about it. Click the photo for a postcard-type view of this end of the lake taken last weekend.

A fault runs through it: Montclair

The Hayward fault runs through the heart of Montclair, in the Oakland hills behind Piedmont. Montclair Park’s duck pond was constructed where the fault left a natural sag in the ground.

Only in seismologists’ equations, and perhaps deep down in the crust, are faults smooth, flat planes. In the world, on the surface, faults are as ragged and variable as any other geological feature. The Hayward fault is more of a zone, from a few to a hundred meters in width, with several fractures running through it. Where two strands overlap, a block of ground between them may slump in tension or rise in compression, depending on how the strands are oriented. At Montclair Park, two strands are mapped on either side of the sag basin. Lake Temescal is another example of a sag basin repurposed as a water feature. So, apparently, is Lake Aliso, the pond on the grounds of Mills College.

The first “great San Francisco earthquake” occurred 21 October 1868 on the Hayward fault. The epicenter appears to have been in southern San Leandro, and surface rupture extended from there all the way down to Fremont. In Montclair, the other direction along the fault, there was plenty of shaking of course, but no rupture of the ground from what we can tell. A trenching study, conducted along the third-base line of the little ballfield in Montclair Park, found no sign of recent movement along the fault there. But slow, silent motion does affect the fault in Montclair. The old fire station on Moraga Avenue has been rendered useless by aseismic creep, and some of the houses along the fault appear to show foundation disruption. But generally creep is invisible unless there is some structure that it affects, like the south curb of Medau Place, below. South of here, the fault crosses Route 13, reaching the other side at the head of Dimond Canyon.