Lower Diagonal starts just to the right of the big dead tree stump. Climb up the crack to a ledge. At the ledge, follow the lower diagonal crack (less defined than the upper) to the corner of the buttress, then climb up the corner to the top.
Similar to leading "Chicago" in that there are not a lot of good stances in a sustained crux, the gear is off to one side, and it takes some work to figure out gear that is good. Must have been a real hero climb in the days of the piton!
From the old guidebook, "Climbers and Hikers Guide to Devils Lake" by David Smith and Roger Zimmerman, 1970:
"LOWER DIAGONAL, F8B. This route offers experience in placing pitons on the run. Start the same as Birch Tree Crack. Climb the crack to ledge (A) exit left to the upper section of the Pedestal. (A) THE TRICK, F9A. Climb or attack (indeed, a battle will ensue) wall above directly. First lead by Jim Erickson. First lead of the Trick by Sheldon Smith."
Interesting that almost no one uses the Birch Tree start anymore.