An appealing looking line whose guidebook difficulty and severity ratings of 5.11C S both understate the case. I tried leading Tanquerey immediately after leading Sidewall and found T far harder and more dangerous.
This climb is the right of two clean, hanging, right-facing dihedrals about 30' right of Xanadu on the upper West ridge. To get to the dihedral, you can face climb straight up to a ledge with a tree (easy 5.10, limited pro, suspect rock) or climb easily up a crack system about 10' right of the corner line and traverse in at the level of the ledge; if you take the 2nd option, beware of a horrible death block -- a 100+ lb rock tenuously perched on a sloping slab.
From the ledge, you can get some good small pieces in the start of the corner which allow you to access a smaller ledge about 8' up. Perform a tricky mantle (10-) protected by a couple of RPs onto the smaller ledge. Once standing on the 2nd ledge, reach high and place a #2 RP; ensure the solidity of this piece as it is probably all you will get through the crux -- if it blows, you will probably hit the tree ledge. The crux is the 10' after the small ledge. The left wall is vertical, has no footholds and a few disappointing handholds. The right wall is slabby, has a few foot nubbins and no handholds. There is at least one decent protection opportunity for a small RP in the crux, but good luck stopping to place it. The pitch ends at a substantial ledge about 60' above the ground. A rap anchor exists on a tree in the crack system to the south, about 10' below and 10' to the south of the belay.
Note if you find yourself midpitch, unwilling to commit desperate, tenuous stemming with a single #2 RP between you and the ledge, it is easy to traverse to the crack on the right, climb it (easy 5th class) traverse back to the Tanquerey belay, and rig a top rope.
This route is more serious than the S rating would imply -- S+ or S/VS is more like it. Take a light Eldo rack w/ plenty of RPs. Screamers would increase the safety factor
Tr'd this after Xanadu yesterday, and I agree that the lead would be a heady one! At the crux, you are kinda pretending that there are holds while steming your way up. Super insecure and if you blow it you would hit that ledge well before the rope starts to catch. Fun, thin climbing though on TR.