Detail of the rock garden in Ruth Asawa's 'Garden of Remembrance' at UCSF. All photos by Andrew Alden.

Stone is more than the peculiar specialty of geologists. All of us have dealt with stone since our deepest ancestors' days in the African savanna, and I welcome the variety of viewpoints that center around it. The child, the builder, the fabricator, the gravestone cutter and the artist see stone in special ways. Lately I've noticed the affinity for stone that Ruth Asawa displays in her art.

Ruth Asawa has created public art in the Bay Area and elsewhere for more than 40 years. Unlike her signature woven wire pieces, Asawa's public commissions are in bronze or stone. The bronze is carefully sculpted and cast, but the stone is as nearly natural as can be. Let's look at two interesting examples in San Francisco.

The Buchanan Mall (Nihonmachi) Fountain is an installation meant for use and enjoyment as an integral part of the Japantown center. It immediately calls to mind the traditional Japanese rock garden in the streamlines of its cobblestone pavers and island stones.

Bronze sculptures, one of them a fountain, sit in two stone circles like islands or ponds. Both were inspired by origami.

Both circles include island stones and are harmoniously faced with Californian river rocks. It interests me that Japan and California, facing each other across the Pacific, both owe their geology to subduction, the plate tectonic process of clashing plates that pushes their rocks together into mountains.

The Garden of Remembrance is in a courtyard at San Francisco State University, built to commemorate the imprisonment of Japanese-Americans during World War II—a troubling act of U.S. public policy and a formative event in Asawa's life. It has two parts, a grassy square and a waterfall rock garden.

Apparently Asawa's intent for the square was to bring together rocks from each of the ten War Relocation Centers. But the first stone I approached told me immediately that geology had thwarted this purpose.

This classic peridotite, streaked blue with serpentine minerals, could not have come from California's Tule Lake or Manzanar. The first would have been black Cascades lava, the second Sierran granite or gneiss. This boulder comes from the Klamath Range. Clearly these stones were symbolic, not literal representatives of the camps. It was a relief at that point to put down my geologist's mindset, because an artwork like this should not distract anyone from its true purpose.

Later I learned that the Rohwer, Arkansas, camp where Asawa spent the war years (along with George Takei, Janice Mirikitani and more than 8,000 other American citizens) was located in a marshy lowland with no rocks at all. The same was true of the camp at Jerome, Arkansas.

While there is some color among the ten boulders, most are structureless mudstones, dark and mute. They populate their lawn in a scatter that schematically matches their pattern on the American map. (In that context, the blue peridotite represents Tule Lake and its exceptional role in the camp system. Maybe my geologist's mind has something to work on after all.) Asawa collaborated with stonesetters Isao Ogura and Shigeru Namba in selecting and placing the stones here, and in the uplifting rock garden next to the lawn.

Even at shady times of day or in the typical fog, this garden must be a bright place thanks to the light-colored Sierran boulders. On a sunny day, the combined direct and reflected light makes it almost dazzling. The top photo of this post shows a closeup. The stones themselves are luscious, coaxing even the geologist to simply stand and gaze.

^{Sutro Tower and the gnarled chert of the Marin Headlandsterrane are parts of a splendid spectacle at San Francisco's Corona Heights. Photos by Andrew Alden.}

San Francisco is "America's Favorite City" for many great reasons. Geologists have their own list of reasons to love it, many of which are Franciscan—by which we mean the peculiar association of rocks found up and down the Coast Ranges. Corona Heights is a small hill west of the Castro district that features some of these rocks, but one of its main attractions is a world-class slickenside.

You get to Corona Heights by walking about a mile west from the 16th/Mission BART station, or by taking the F line up Market Street to the Noe or Sanchez stops. Here's the hill as seen from 16th Street. You can't miss it.

Corona Heights is a hardworking hill that formerly yielded clay and chert. Years of quarrying have accentuated its rugged appearance and left splendid exposures of the bedrock. Along the way, if you keep an eye on appearances of old concrete (doesn't everybody?), you may spot the old chert aggregate around the neighborhood.

Corona Heights, like Bernal Heights to the southeast, is an island of resistant chert that is part of the dismembered Marin Headlands terrane. It houses a fine playground and the Randall Museum. It has a dedicated group doing habitat restoration. But we're here to see the slickenside.

A slickenside is the polished surface that is created along a fault as the rocks rub against each other. They are common in faulted rocks, but only in patches the size of your hand. (I showed you some in the Calera Limestone.) Larger ones are rarer. Quarrying at Corona Heights uncovered one the size of a big front yard, one of the world's largest exposures. To see it, start at Castro and 15th, go uphill on 15th and turn left on Beaver Street. Again, you can't miss it.

The site is also a playground, named for Sidney Peixotto. If you continue up 15th Street instead, you'll see the exposure this way.

But the real joy of the thing comes at close hand, where you can feel the mirror-smooth surface that only a hard stone like chert can provide.

Surfaces like this are of scientific interest, although the data base is still scant. UC Santa Cruz researcher James Kirkpatrick has surveyed this site by lidar. He and others hope that close analysis can tell us more about how faults behave in detail. That's an advanced topic; the rest of us can collect the geocache at this spot.

Afterward is a good time to climb to the top of the hill and take in one of the city's best views. On a clear day you can see Mount Diablo (click for a 1000-pixel version).

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Hack for Change comes to SF this June

On June 18th and 19th, 50 lucky developers will convene in San Francisco to spend 24 hours building developing mobile applications that are meant to leave our world better off.

Hack for Change is an initiative of Change.org, a website that helps people create and dispense online petitions.

As Hack for Change mentions on its site:

"Through technology we have the potential to democratize politics, to hold power accountable, and to find innovative solutions to the world’s problems.

So, we’re inviting 50 engineers and designers who believe they can make the world a better place to spend 24 hours to build a web or mobile app that can help advance positive change."

Winners will receive $10,000 which is meant to help continue building out their application.

Want to get involved? Teams and individuals are eligible to snag a seat at Hack for Change. Whether or not you have an idea to start working on, there are lots of suggestions on their site along with teams to pair up with at the event. Submit an idea or sign up for Hack for Change here.

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 The Changing Bay Educator Guide

Peer into San Francisco Bay and you probably won't see much, thanks to the murky water the bay is known for. But over the past decade, scientists have made a surprising discovery — the bay's water is clearing. As Lauren Sommer reports, clearer water is not always good news.

Sittin' on the dock of the bay, watchin' the tides roll away.

This is important because the bay and ocean currents flooding in and out of the Golden Gate are notoriously treacherous.  The US Government realized early on the importance of San Francisco Bay and the need to better understand the movements of the water for navigation.  Soon after California became a State, American surveyors were sent to San Francisco to study the water conditions of the great port.  And the work has continued non-stop ever since.  For over 150 years the San Francisco Tide Station, now operated by NOAA, has produced a continuous recording of water levels and other vital maritime information.

Today the tide station uses state of the art equipment to measure the water movement of San Francisco Bay. The water gauges are connected to the NOAA Physical Oceanographic Real-Time System (PORTS), and measure nearly real-time water levels, surface and sub-surface currents and other information such as winds, weather and climate data.  This information is available to the public so sailors know the best times to cast off, make transits, load or unload cargo, or when to ride the tides in or out of the bay.  According to a report written by Captain Albert E. Theberge, NOAA (Ret.), “This information is critically important considering that there is an average of 261 deep-draft vessels entering San Francisco Bay each month and there are approximately 85,000 registered pleasure boats using approximately 100 yacht clubs in the Bay system.”

“The historical record from the tide station at San Francisco transcends the maritime history of the San Francisco Bay,” according to Captain Theberge.  “From the days when clipper ships relied upon tide predictions provided by the station to navigate the dynamic waters of the Golden Gate, to the modern day mariner that obtains real-time water levels so that the huge ship and crane barge operators can tell if they have enough depth in the channels and enough clearance under the bridges.”

In the process of collecting data to insure safe passage in and out of the bay, the San Francisco Tide Station has been instrumental in collecting a long and continuous stream of scientific data that has advanced our knowledge of the oceans and the earth. This data has benefited meteorologists, oceanographers and climatologists alike.  As we look to the future and attempt to better understand the changing climate and what that will mean to things such as sea level rise, the current and long-term data collected at this small station will become increasingly more important.  “San Francisco is an amazing city in terms of its heritage,” says Mary Jane Schramm, “ The human heritage as well as the magic and mystique of the great Golden Gate.  It’s a portal for exploration.  We are explorers and by virtue of having this facility here helps foster that process along.”

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Seafloor under the Golden Gate Bridge, USGS

Seafloor mapping of the San Francisco Bay and surrounding areas by marine scientists at the U.S. Geological Survey Pacific Coastal & Marine Science Center and Cal State University at Monterey Bay's Sea Floor Mapping Lab (SFML) is important for keeping shipping lanes safe, understanding pollution dispersal, mapping habitats, and much more.

Mapping of the underwater topography (called bathymetry) reveals landscapes fundamental to understanding the Bay Area's unique geology. The Golden Gate strait connects the San Francisco Bay to the open Pacific Ocean and is only one mile across.

Although the tidal range in the Bay Area is not incredibly large, the narrowness of the Golden Gate creates a funneling effect:

"Large volumes of water move into and out of San Francisco Bay as the tidal level of the Pacific Ocean just outside the Golden Gate changes each day. When the tide is changing from low to high levels, a flooding current moves water inland from (and through) the Golden Gate. When the tide is changing from high to low levels, an ebbing current moves water from inside the Bay toward (and through) the Golden Gate."

The image above (from Cal State Monterey Bay) is a perspective image looking towards the east. The colors represent water depth with the reds and yellows as shallower water and the blue and purple deeper water. The prominent patterns in the foreground might look like ripple marks on the beach, but these sand waves are similar in scale to some sand dunes seen in deserts — up to 30 feet tall and more than 700 feet from crest to crest.

The vigorous currents funneled through the Golden Gate continuously move sediment from underneath the bridge where it accumulates as these sand waves. But remember, this is a static snapshot of very dynamic systems. I'd love to see multiple repeat surveys that show how the field of sand waves change over time.

Learn more about the processes that move this sediment from this USGS article and in this SF Chronicle piece from 2006, along with this QUEST story on 3-D seafloor mapping.

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Images: (1) From USGS Scientific Investigations Map 2917, Under the Golden Gate Bridge — Views of the Seafloor Near the Entrance to San Francisco Bay; (2) Cal State Monterey Bay Sea Foor Mapping Lab

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Although it may not be obvious at first glance, the bay side of San Francisco is largely artificial. The huge increase in population associated with the California Gold Rush of the mid 1800s resulted in San Francisco becoming the major port on the west coast. In some cases, people seeking riches in the Sierra Nevada headed off to the mountains and simply abandoned their ships in San Francisco. Some of these ships ended up being used as landfill and, year after year, the shoreline along the northern and eastern sides of the city was modified.

The area where Market Street meets the Embarcadero was among the earliest areas to be extended into the bay, but landfill — a combination of sediment dredged from the bay with rubble — continued to be used to create new "land" for decades to come.

The map below* shows this modification quite nicely. Original creeks and streams are in blue, marshes in aqua-green, and modern landfill in pink.

What I like about this map is how the pink landfill areas highlight the old shoreline. Note where the original creeks and marshlands met the bay. What is now a relatively straight shoreline was once very irregular with several natural embayments. Mission Bay was once an actual bay. I find it fascinating to picture the city in this way — the way it was a little over a century ago.

The areas that are now landfill are important to consider not just as interesting history, but also in the context of earthquake hazards. Last week I discussed Bay Area seismic hazard preparedness and an important component of getting ready is to learn about how different types of land respond to the shaking.

The map above** was produced by the USGS and shows the liquefaction hazard — red is very high hazard, orange is high, yellow moderate, green low, and no color is very low. Liquefaction is essentially when loose sediment behaves like a fluid when shaken, which can result is serious damage to buildings and houses.

Note the correspondence between the red areas on the liquefaction hazard map with the map showing where landfill and old marshes are. While it may seem like solid ground when you are walking or driving on the street it's important to remember that the fill underneath is quite loose compared to actual bedrock.

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* This great map, and many more, can be found at the website for the Oakland Museum of California: http://museumca.org

** See the entire zoomable map, learn more about liquefaction hazard, and how the USGS made this map here.

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Quest Educational Resources

 Print Guide - Big Break Regional Shoreline Science Hike

 Big Break Regional Shoreline KML file

 Tips to get the kids in your life out into nature

 Designing an Exploration on Google Maps

Additional Links

• EBRPD – Big Break Regional Shoreline
• Pacific Flyway Council
• PRBO:Tracking Migrating Shorebirds