California 99 is the main north-south corridor through the eastern Central Valley. Much more populated than the western side of the Central Valley, the eastern side is home to cities such as Bakersfield, Visalia, Fresno, Madera and Modesto. California 99 passes directly through these cities, while Interstate 5 bypasses to the west and does not come close to California 99 until near Manteca and Stockton.
California 99 is the original route of U.S. 99, which was decommissioned in stages starting in 1964. Old alignments of the original route are preserved as business routes in the urban areas, and the freeway was continuously upgraded to six-lane freeway standards.
California 99 approaches the Bakersfield area from the south. Splitting with Union Avenue, which is the historic route of U.S. 99 through the city, California 99 stays west of Downtown Bakersfield. Union Avenue travels through the city center and provides access to most businesses. Joining with California 99 near the business district is California 58, which originates from the California Central Coast to the west and travels east through Bakersfield and Tehachapi Pass into the Mojave Desert.