A 104-page “Legal Memorandum” accompanying EPA’s proposal of §111(d) Existing Source Performance Standards for Electric Generating Units under the Clean Air Act charts the legal waters the Agency will have to traverse if it adopts rules anything like those it proposed. The need for so comprehensive a map arises because EPA proposes a voyage far away from where §111(d) has ever sailed. But unlike the 16th-century explorers who ignored the dragon warnings at the edges of their maps, here EPA actually will encounter the identified dangers, which are so great as to reduce to near zero EPA’s prospects for safe crossing to its intended destination.