I’m standing at the corner of Blackstone Court and Franklin Street in San Francisco’s Cow Hollow district. There’s not much to see, just an alley that runs for a half-block or so between the back of a motel and a dentist’s office, with some old houses partially hidden behind a tall metal gate at the end. Curiously, though, the alley is off-kilter from the surrounding streets, running at an angle of about 20 degrees from the street grid. Few passersby are likely to notice the misalignment, but it’s a clue to a vanished landscape: Blackstone Court follows an old trail that in the 1850s and 1860s ran from town out to the Presidio, skirting the north end of Washerwoman’s Lagoon, an important freshwater source for early San Francisco. In 1882 the lagoon was filled in, and as the city expanded a new street grid was laid overtop, erasing most evidence that the lake ever existed--except for Blackstone Court.

Here in the sea of concrete that is modern-day San Francisco, with the sound of cars and trucks on nearby Lombard Street roaring in my ears, it’s pretty much impossible to imagine that earlier, far more bucolic landscape. Certainly it would never have occurred to me that an oddly angled alley could point the way to an old lake where shirts were scrubbed and cows came to drink. But such details leap out at Christopher Richard and Janet Sowers, who since the early 1990s have been piecing together the contours of the Bay Area’s past and present watersheds and waterways for the San Francisco Bay creek-mapping project of the Oakland Museum of California (www.museumca.org/creeks). Blackstone Court is just one of the clues they found as they researched the San Francisco map, published in June.

Richard and Sowers’s first map, published in 1993, was of the Oakland and Berkeley watersheds (see Coast & Ocean, Vol. 13, no. 1). Ten more have followed, covering most of the east, south, and west shores of the Bay. One for San Mateo is due out early in 2008, and if funds permit, the series may be continued through the North Bay.

Sowers, a senior geologist with William Lettis & Associates, a consulting firm, and Richard, curator of aquatic biology for the Oakland Museum of California’s natural sciences department, have guided the development of most of the maps, collaborating with others from the Museum, Lettis & Associates, the San Francisco Estuary Institute, and the Bay Institute.

Of all the maps in the series, Richard said, “San Francisco has been the biggest challenge, because urbanization began before accurate mapping” was undertaken. When the U.S. Coast Survey showed up to map the area in the early 1850s, many of the city’s wetlands had already been drained or filled. There may be more historical references available for San Francisco than for other Bay Area locales, Sowers said, but “because there’s a longer history, there’s also a longer history of alterations.”

Secrets beneath the Sand
The city’s geology also made the job more challenging for Richard and Sowers. Before it was paved over and built up, more than half of San Francisco was covered by sand dunes. Bedrock poked through on the hilltops, the higher peaks sheltered a few areas from the blowing sand, and along the Bay shore there were marshes, estuaries, and tidal sloughs. Everything else was sand, sand, sand. “In other parts of the Bay Area, the topography gives you a very good idea of where the creeks ought to be,” Sowers said. “But in much of San Francisco, the topography is not due to stream erosion, but to sand dunes.” Sand still underlies much of the city.

Dunes don’t typically support significant surface streams. Instead, water percolates down and moves underground, popping up here and there in low-lying areas as a pond or wetland. Mobile sand dunes block off creeks, creating more ponds. So San Francisco circa 1850 didn’t have many major creeks, but it did have a surprising number of freshwater ponds, lakes, and wetlands among the dunes. (Some of these ponds still exist in Golden Gate Park, though they have been modified.)

Also complicating the mapping of waterways was the city’s combined sewage and stormwater system. Every other city in California (except for portions of old Sacramento) collects its sewage in one set of pipes and sends it to a treatment plant, while stormwater runs through separate drains, typically directly into lakes, creeks, or the ocean. (Many cities are now studying ways to upgrade these systems, due to stricter water-quality regulations mandating that runoff be treated.) Because most of San Francisco’s sewers were built before sewage treatment existed, the city still collects both sewage and runoff in the same pipes, but today the effluent is pumped into massive tunnels, known as transport/storage structures, that were installed between the 1970s and 1990s and run along the city’s entire shoreline like a moat.

The system essentially divides San Francisco into two “sewersheds”--drainage basins defined by high points from north to south. From these points, all sewage and runoff flows either east or west to the transport structures, which then carry it to treatment plants. “In dry conditions, everything east of Twin Peaks goes to the Southeast Treatment Plant [near Third Street and Evans Avenue], and everything on the west side of Twin Peaks goes to the Oceanside Treatment Plant [near the San Francisco Zoo],” Sowers said. (The exceptions are the Presidio, which drains to the bay, and Golden Gate Park, Lake Merced, and Stern Grove, which drain directly into the ground.) Another plant, the North Point Facility on Bay Street, provides additional treatment capacity during wet weather.

“Conceptually, the watershed model breaks down when you’re pumping water between watersheds,” Richard said. “Defining exactly what a watershed means becomes a lot more difficult. The combination of sanitary sewers and stormwater drains made the [mapping] project more interesting and challenging.”

During major storms, the combined system can overflow, in which case the runoff will follow something resembling the historical creek watersheds, flowing to the Bay or the ocean. The “watersheds” indicated by different colors on the Oakland Museum map are areas that drain to a particular channel (such as Mission Creek Channel) or stretch of shoreline during these events. Unfortunately, when that happens, sewage that is only partially treated is released into the Bay or ocean, though this occurs less frequently now than it did before the transport/storage structures were built.

The reverse side of the map contains text, photos, and maps explaining the original dunescape and historical ecology of the city, prepared by Robin Grossinger of the Estuary Institute, and additional information about the combined stormwater/sewage system, created with the help of the California Public Utilities Commission (PUC).

Seeing the Lay of the Land
Sorting out the historical and built watercourses was often a daunting task. For example, many anecdotal sources referred to Hayes Creek, which is said to have flowed through Hayes Valley and what is now the Civic Center down to the marshes around Mission Bay. But when Richard and Sowers set out to chart its course, they could not find it on any historical map. The only evidence for a creek lay in the contour lines on topographic maps, whose V shape indicated a valley--eroded, presumably, by a creek--that sloped toward the Bay. The fact that much of Hayes Valley was originally covered by sand dunes led Richard and Sowers to conclude that the creek was probably ephemeral--flowing underground through the porous sand for most of the year, and on the surface only after heavy rainstorms. Early mapmakers may have seen no creek in Hayes Valley. Today the area is largely paved, and most runoff goes down the storm drains and into the combined system.

Yet plenty of water still percolates underground in the area. For years, Richard has heard stories about water pouring into nearby basements in the rainy season, and when the San Francisco Conservatory of Music was renovating its building at 50 Oak Street, he said, you could look down into the hole and see the water. “They had to pump water 24 hours a day to keep [the hole] from flooding.”

With most of San Francisco’s natural landscape so resolutely buried, it takes special skills--and a special kind of awareness--to discover where the water once flowed and pooled, where it seeped inland into marshes and sloughs or bubbled up from underground aquifers into ponds nestled amid the sand dunes. It’s clear that both Richard and Sowers enjoy the hunt. When you ask them about finds like Blackstone Court, their eyes light up and they start pulling out maps. “It’s fun to piece together the history of a place, what it was like and how it has changed,” said Sowers.