The board of supervisors of any county owning fairgrounds and fairground facilities may (a) lease, let, or grant licenses for the use of its real estate or personal property or any portion thereof to private individuals or associations for whatever purpose may be approved by said board, which will not interfere with the use of such property for fair purposes; and (b) arrange for and conduct or cause or by contract permit to be conducted by another individual, institution, corporation or association, upon such property at such time as it may deem advisable, any activity which will not interfere with the use of such property for fair purposes.