To approach the Firing Squad park at the "S Curves" in Big Cottonwood Canyon and hike up the road along the creek to the Mill B trailhead. From here follow the summer trail up the drainage through the aspens on the E side of the creek. This trail sees lots of traffic so it's most likely a well trodden path at least up until the lakes. From the lakes you'll want to head SW up the undulating rolling hills until you reach the upper basin. Once there you should be able to see the peak and wind your way through the cliffs and benches that lead to the peak. This is a large avalanche prone slope so make sure conditions are solid. Gain the summit and find your way into the line.