The right-hand side (arete) of the blockhead boulder. With your right hand on the arete, use edges and slopers with the left hand to top-out. A good problem that will become much better with some traffic.
Lord Blockhead is 0.55 miles from the Shelf Road parking lot on Gridley Road. Having parked at the Shelf Road parking, hike up the road for 0.28 miles. Leave the road and take the single track heading steeply uphill on the right. Continue following the single track uphill and up the ridge for another 0.27 miles (this part takes a while due to the steepness of the trail) until the trail passes between the Blockhead Boulder on the left and the Californio boulder on the right.