43 Miles south of Columbus in the Custer National Forest. From Columbus go south on MT 78 to Roscoe (about 29 miles). At Roscoe head west on East Rosebud Road and follow it into the canyon. For more info refer to "The Rock Climber's Guide to Montana by Randall Green.
Mountain Project's determination of some of the classic, most popular, highest rated routes for East Rosebud Lake: