Big Rock Boys Mantle

Just right of "Borson's Mantle" is a roughly-triangular-shaped sloping shelf listed as 5.12 in the Craig Fry guidebook. Apparently the idea is that one could mantle this, but I've never seen anyone do it in seventeen years of climbing here. Perhaps equally astonishing is that Big Rock's "testpieces" presumably gave these boys (whoever they are) the requisite skills to power off this move.