David Baker Architects


Making Big Moves at Mason on Mariposa

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Mason on Mariposa. Image: Adam Potts

By David Baker, FAIA, LEED AP

The site's history, topography, and neighborhood context drove the design.

See more about Mason on Mariposa here

If walking along the paseo greenway that runs through Mason on Mariposa feels like floating down a creek, that is no coincidence. Winding between new urban homes, this meandering open space takes its form from, and in a way resurrects, the free-flowing landscape of the site’s past.

A new micro-neighborhood tucked into the base of Potrero Hill, Mason on Mariposa realizes the full potential of an under-used site by responding to its history, topography, and the varied characters of its neighbors—industrial, residential, institutional—on each side. The broad generous greenway that drives the organization of the site traces the path of a long-disappeared stream, a vestige of the past that provided inspiration and created opportunities now and into the future.

History and Discovery

In the summer of 1962, fire broke out in the timber supports of the Western Pacific railroad tunnel on San Francisco’s Potrero Hill. Portions of two streets, 19th and Arkansas, caved in, taking a few houses with them. Eventually, the tunnel was filled in, weeds overtook the site, and the hillside site became a wild place and impromptu dog park, with no trace of its former life.

DBA first stepped in the 1990’s when Holliday Development purchased a portion of the abandoned site at the top of the steep slope, with the hopes of building new housing. We designed the g2 Lofts—affordable live/work artist live work lofts, complete with a gallery, studio, and performance spaces—plus 18th & Arkansas—30 market-rate lofts facing 18th Street. When the contractors started digging for 18th & Arkansas, they unearthed an unmarked three-foot-diameter pipeline. Apparently, the railroad tunnel, which we knew about, had been built over an undergrounded creek, which we did not. This pipeline provided a challenge for our project. We were able to slightly reroute a small section of it for our site at considerable trouble and expense, yet it was clear the issue would resurface in the future development of adjacent sites.

18th & Arkansas/g2 lofts completed in 1995. Image: David Baker Architects

New Life for an Old Site

Two decades later, 18th & Arkansas had become a fixture of the neighborhood, and Related California purchased the facing land on the block to the north of 18th & Arkansas, as it slopes down the hill toward Jackson Playground. Related brought DBA onboard to design the mixed-use Mason on Mariposa. This property had borne a number of industrial uses over the years and at the time included a defunct bus yard and auto repair facility. Significantly, as we now knew, it also contained the hidden pipeline encasing the creek, running at an angle across the entire site.

So the first step in designing Mason on Mariposa was to address the pipe. Moving it would have been prohibitively expensive, so we chose to embrace it. The San Francisco Planning Department’s Eastern Neighborhoods Rezoning and Area Plan allows pedestrian pathways that are at least 40-feet wide to count toward a project’s open space requirements, so we created an easement for a broad passageway that runs north-south from the middle of the 18th Street block to Mariposa Street, right across from Jackson Playground. We gave the center of the site “back to nature,” then organized the residential buildings and amenities along this broad passageway that followed the path of the original creek. This slanted passageway also created irregular shapes for the buildable site, which required creative design approaches and resulted in organic-feeling angles to the buildings.

Site Plan: Active ground-floor uses, with a new public pedestrian greenway connecting 18th Street to Jackson Playground. Image: David Baker Architects

The central paseo became the heart of the project, and was brought fully to life with the collaboration of super-creative landscape architect Fletcher Studio. Fletcher Studio created a wonderful urban landscape design that defines the greenway, with custom fencing, sculptural seating, young cherry trees, and “social eddies”—pooled plazas along the path that inspire pausing and gathering. Cut basalt columns represent “snags” along the lines of the historic stream bed while doubling as playful seating options.

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Paseo Greenway with basalt columns. Image: Craig Cozart

The success of the broad paseo inspired the way Mason on Mariposa related to the adjacent Live Oak School, an existing private school at the northeast corner of the block. Instead of building housing right up to the property line, we proposed a 40-foot setback from the school, which took the form of another public pathway that runs behind the school, connecting Arkansas Street with the paseo greenway.

The Planning Department and the neighbors loved the idea—a win-win for us! Because the setback exposed an area of the garage to daylight, we were able to convert that area of parking to housing. The setback also gave the northeast units views of a landscaped pedestrian path. We upgraded the Live Oak School's windows, so they could enjoy the glimpse of greenery as well.

Topography and Texture

Mason on Mariposa inserts a large development—299 homes, 20% of them affordable—into the fine-grained fabric of Potrero Hill. The varied topography of the site, on the north slope of the hill, allowed us to bury different elements of the program and turn the majority of the open space back over for public use. Embracing another artifact on the site, we used the defunct bus garage as a shell for our parking garage, taking advantage of the excavation into the hillside and the existing retaining wall. This reduced cost and demolition, and preserved the site's edges for active uses.

The neighboring typologies vary widely at each edge, from the industrial west to residential southeast on Arkansas Street, which has 25-feet lot widths. For 18th & Arkansas, we created walk-up flats that matched this lot width to fit into the neighborhood. As we began to design the edges of Mason on Mariposa, we photographed the facing street elevations and did typology studies to determine how to address each edge.

Elevation typology studies along Arkansas Street. Images: David Baker Architects

Along the steep climb of 18th Street, we matched the elevation of our 18th & Arkansas Lofts. However, we set the newer building a bit lower so as to preserve views to downtown San Francisco. Along the more residential Arkansas Street, we drew the building back five feet from the property line and articulated the massing and materials to suggest separate townhouses. We connected these homes to the sidewalk with private stoops. It feels very much like the existing neighborhood, but with fewer curb cuts, so there’s actually more street parking than what is across the street.

At the lower, more accessible northwest corner, the site connects to Showplace Square, the playground, and the giant grain silos of the Anchor Steam Brewery. Here we placed a mixed-use building with a retail ground floor that faces the playground and serves as the main entry point for the property. This edge features a live/work-style elevation and incorporates local commercial and retail space on the ground level, with landscaping and seating. The units on this side are zoned for production, distribution, and repair (PDR), so there is the opportunity for a range of dynamic uses on this street.

This complex project was created through a lot of community conversation, innovative approaches, technical skill, and creative collaboration. Related California developed the property and contributed $2 million to neighborhood infrastructure and park improvements. BAR Architects designed the distinctive mixed-use retail building that anchors the community at the corner. Executive architect Ankrom Moisan brought the buildings to fruition. And Fletcher Studio’s inviting and imaginative approach to the paseo greenway breathed life into the site and stitched it seamlessly into the base of the hill.

In a recent article, The SF Chronicle’s John King likened Mason on Mariposa to “a new thread in a comfortable fabric,” praising the new community's successful integration into the neighborhood.

Fully realized, Mason on Mariposa draws on a forgotten past to weave itself into the neighborhood, hopefully becoming a fixture that influences surrounding development well into the future.


David Baker, FAIA, LEED AP, is a Principal at DBA. He founded David Baker Architects in 1982 and is considered an industry leader in urban and affordable housing design. You can contact David here