The proposed Keystone XL Pipeline would start in the town of Hardisty, which about a hundred and twenty-eight miles southeast of Edmonton. It would cross the Canadian-U.S. border in Montana, jog through western South Dakota, then head down through Nebraska, Kansas, and Oklahoma all the way to refiners on the Gulf Coast. The pipeline, a thousand seven hundred and two miles long, would carry crude from what supporters call the oil sands and critics the tar sands—a huge deposit of very heavy hydrocarbons in central Alberta. (I wrote about the Alberta tar sands for The New Yorker in 2007.)