As Sarah notes, we've not seen any regs in the national parks stating no clothesline and have never been asked to take one down. The big thing is locking up in the car (or in a bear box) all food and any thing that remotely smells of food (like toothpaste) . This keeps the bears and skunks away... We're very careful about dishwater as well (it gets poured down a toilet or dump station) as dishwater is a big pest attractant.
Our last day we came across a black bear cub and momma bear while hiking. Fortunately Jr bear ran toward momma, she stood still, and we went on our way making lots of noise. Good bear....
Our last trip I tied the clothesline between the poles of (and under) the REI canopy which, in my opinion, looked better than our hillbilly line strung between two trees. Hammocks look much better tied to trees....
Hey now, easy with the "hillbilly." We prefer to be called Hill-Americans. And that ain't no clothesline, that there's one of them there solar close drars.