Marta's family had built the retaining wall stone by stone, starting at the bottom-left corner and working up and to the right. Five generations of masons. The wall filled their survey grid completely — a perfect square of dressed granite. Then the tremor split it along the old fault, the one her grandmother had warned about: a crack running from the top-left corner to the bottom-right. Everything above the fault line — the upper-right triangle — sheered away and fell. The lower-left triangle, keyed into bedrock, held. It took Marta two years to rebuild what the mountain had taken in eight seconds.