On the stretch of Irving where the N-Judah rattles past the produce stands, Martha Ehrenfeld has the kind of local knowledge that takes decades to accumulate and a particular personality to bother with in the first place. She can tell you which corner has the volunteer nasturtiums coming back every spring, which neighbor planted the tree that's slowly winning its argument with the sidewalk, and — if you've been to enough community meetings — she probably already knows your name.

Ehrenfeld is the president of the Inner Sunset Park Neighbors, a role that sits somewhere between municipal watchdog and block captain, and she came to it the way most people come to neighborhood associations: she cared about something specific, then couldn't stop caring about the next thing, and the thing after that. Plants, in her case, are something of an entry point — the Inner Sunset's fog-friendly microclimates produce a genuinely strange variety of front-yard botany, and she has opinions.

What she describes as being "the perfect amount of nosy" sounds, in practice, like sustained attention. She notices when a storefront goes dark, when a new family moves in, when the park furniture gets rearranged without explanation. This is, more or less, the job description for anyone who wants a neighborhood association to function rather than just exist on a dot-org domain.

She's also candid about the social mechanics of it: it helps, in the Inner Sunset, to know people, and the easiest way to know people is to have a dog. Ehrenfeld doesn't. She found other ways in — meetings, mostly, and the particular willingness to introduce yourself first.

Tomorrow, walking past Grandview Park or down 9th Avenue toward the panhandle, you probably wouldn't spot anything that marks her work directly. That's somewhat the point. The visible change she tends to notice is the one that almost happened and didn't.