A tonneau system for a cargo box of a vehicle having a support frame connectable to the cargo box. A cover spans the support frame and is positionable between a tensioned position and an untensioned position. A pivot block is mounted to the support frame, while the cover is coupled to a rear bracket member. The rear bracket member carries the cover and pivotally engages the pivot block such that the rear bracket member rotates between a raised position and a lowered position. The rear bracket member can be automatically locked in the lowered position. A bow member couples the cover along a cross vehicle direction. The bow member or other member can operate to tension the cover in the cross vehicle direction.