Soil movement would show up as sticking doors and drywall cracks at corners of windows and doors. Any stucco damage or crown molding distress? Damage only at ceiling wall interface? Vegas, I would first think differential thermal movement of very hot attic and south/west walls. Is damage concentrated S and W? Drywall trade is the worst. Usually just poor workmanship of the tape joints or minimal screw attachment of the drywall to the framing. Photos?