Moving to Central Contra Costa, CA? Check out apartments for rent in San Marcos, a metropolitan neighborhood near Central Contra Costa, CA? Residents of San Marcos may prefer to have access to a car, because 87% of residents commute to and from work by car. Getting to and from work takes about 20 minutes. Residents are highly educated, with a large number having postgraduate degrees. For renters who prefer a quiet neighborhood, less than half of households have children.