The possibility of creating the mural was first brought up in 1974 when Baca was contacted by the Army Corps of Engineers about a beautification project. While Baca was working as a consultant for the Tujunga Wash Greenbelt Project, she was offered the chance to beautify the flood-control channel. The wall along the river was considered an ugly eyesore, or in Baca's view, "a scar where the river once ran". The "Great Wall of Los Angeles" as an idea was more fully fleshed out in 1976 by Baca. Baca chose to do an epic-sized history of Los Angeles county, going back as far as the time of the dinosaurs. She first researched highlights of Los Angeles history on her own.