CAT 745C operator was driving to park at shift end. Drove off designated haul road to cut across fill area and hit 24"" deep ditch. EE bounced up and hit head on the grab bar behind the seat, sustaining a 4"" laceration to back of head. CAT's onboard monitoring system indicated that driver was wearing EE's seatbelt. EE was transported to the hospital where EE received 14 sutures.