Tonneau cover system and lock assembly for a tonneau cover system

A tonneau cover system for covering a cargo area of a vehicle, the tonneau cover system including: a side rail configured to attach to a side wall of the cargo area of the vehicle, the side rail comprising a bottom wall; a cover comprising a plurality of slats, the plurality of slats comprising a tail slat connected to a slat, the tail slat comprising one or more rollers that are supported on a top surface of the bottom wall of the side rail; a lock assembly connected to the tail slat, the lock assembly comprising a first locking device connected to the tail slat, the first locking device comprising a first locking member that is configured to engage a bottom surface of the bottom wall of the side rail to lock or restrict movement of the cover relative to the side rail.