Planning Commissioner Geraldine Steinberg was appointed to the board of supervisors in December 1974, becoming the first woman since Louise Ayer in 1935 to serve on the board. Standing for election in 1976, Steinberg became the first woman elected to the board, joining a wave of other women in public office including San Jose Mayor Janet Gray-Hayes, who was elected in 1974.

Steinberg's involvement in county government began in 1965 when she served as deputy county counsel following completion of her law degree at Stanford University. In 1967, she went into private practice, but her interest in land use issues brought her back to the public sphere. Watching the Permanente Cement Company mine the hillside near her home in the Monta Vista-Los Altos Hills area in 1970, Steinberg and her neighbors began voicing complaints to the county. Steinberg's efforts impressed Supervisor Victor Calvo, who nominated her to replace outgoing Planning Commissioner Lawrence Anderson. As the first woman to be appointed to the County Planning Commission, Steinberg worked to effectively plan direction of development in the county. Though committed to preserving the resources of the county, she believed planned growth was vital to the long-term economic health of the area.

Steinberg was appointed by the board to replace Supervisor Calvo, who was elected to the assembly. After becoming District 5 supervisor, she served on the General Plan Committee for two years, helping to pass a two-year moratorium against subdivisions of unincorporated land until the general plan could be completed. Utilizing her strong skills as a consensus builder, she was able to resolve opposing interests of developers and environmentalists into agreements on ways to preserve the valley's hillsides.

Steinberg was always conscious that her work as the first female supervisor would serve as a model for other women to follow. She was sworn in as the first woman to chair the board of supervisors by Judge Marilyn Pestarino Zecher, the first woman to sit on the superior court bench. In the late 1970s, Steinberg was considered for appointments to the superior court and municipal court, but decided to continue to serve on the board of supervisors.

Demands on her personal time convinced Steinberg to leave political office in 1981, allowing her to return to work as an attorney and to spend more time with her family.