I bet it's a cheaper cousin to the Sears / Huffy Rail and the Huffy "The Wheel", decal on the chain guard is pretty close, same frame but looks shorter, and no gears.
CS stands for cheater slick, a mid range offering sold in department stores etc. It looks like it has a BMA sticker on the seat post tube, these started being used in 1970 or 1971 I think.