It looks like the most likely source of the haze/smoke over Contra Costa County this evening is the Timber Fire in Monterey County, near Big Sur. NOAA satellite analysis from Monday specifically showed the Timber Fire producing heavy smoke that was traveling northward. The fire is still active today at about 15,998 acres and 26% contained, according to CAL FIRE. There may also be some high-level residual smoke from Pacific Northwest and Canadian wildfires, but the Timber Fire is the clearest current California source sending smoke north. NOAA described a broad layer of light smoke over much of the western U.S. as well.