The boards of directors of joint county road camp districts may contract with the State Department of Public Works for the employment of jail prisoners in the construction, improvement, or maintenance of any portion of any state highway now existing, to be constructed, or under construction within said district and may also contract with any board of supervisors or with any supervisor of any road district, within said district, for the employment of jail prisoners on any county road or county public work within any county or road district lying within any district created under this article.