The Great Wall of Los Angeles bears the official title The History of California. But the history it tells is not the one found in standard textbooks. Under Baca's direction, beginning in 1978, more than 400 community youth and artists created a mural that begins in prehistory — mammoths at the La Brea Tar Pits, the creation story of the indigenous Chumash people — and moves forward through colonialism, conquest, and the stories that official history tends to omit.

The panels include the internment of Japanese Americans during World War II, the deportation of Mexican Americans during the 1930s, the Freedom Bus rides of the civil rights movement, the contributions of women to the wartime economy (and their disappearance from it afterward), and the birth of rock and roll. The wall does not shy away from its subject matter. This was Baca's point: the diverse communities of Los Angeles had built California, and the public spaces of California rarely acknowledged it. The Tujunga Wash walls, which the city considered an eyesore, became the canvas for something the city needed to say.

The project ran over multiple summers starting in 1978, funded through a combination of city support, Corps of Engineers cooperation, and community fundraising. In 1981 and 1983, additional phases were funded by a Jewish Community Foundation grant; at another point, the community raised $20,000 in two weeks to help artists complete a section. The young people who painted it — teenagers from neighborhoods across the valley — were paid for their work. Baca viewed the process as education: participants learned math, history, and art while making something that would outlast all of them.

The mural was restored in 2011, with original youth participants returning alongside new artists to put in 8- and 12-hour days on the concrete. It was listed on the National Register of Historic Places in 2017. SPARC — the Social and Public Art Resource Center that Baca co-founded — plans to extend it to a full mile in length when new sections covering the 1970s through the 1990s are complete. Hundreds of additional artists are involved.

Judith Baca has described the Great Wall in terms that distinguish it from decorative public art. "It's not just history, it's really about relationships — about connecting," she said in 2004. In 2000 she was more pointed: "Public art in America has taken a shift; it's basically becoming decorative. They've reduced the community process to censorship. The Great Wall, for example, could not be done today."

The mural stretches along Coldwater Canyon Avenue between Oxnard Street and Burbank Boulevard, covering more than six city blocks on both sides of the wash. It is high, painted directly on concrete. The viewing conditions are not simple — the mural runs in a flood control channel, and a proposed bridge with solar lighting to allow easier access had been estimated at $1.3 million as of 2014. But the work is there, available to those who seek it: a continuous argument, in paint on concrete, about whose stories belong in public space.