On November 10, 2016 about 2345 mountain standard time, a Bell 206B3, N914HH, rolled from an elevated landing pad located on top of a truck and collided with the ground near Yuma, Arizona. The commercial pilot sustained serious injuries. The helicopter, operated by Morris Flying Service L.L.C, sustained substantial damage during the crash sequence. The helicopter was being operated under the provisions of 14 Code of Federal Regulations Part 137. The helicopter departed the landing area about 10 minutes prior to the accident. Visual meteorological conditions prevailed for the nighttime local aerial application flight, and a flight plan had not been filed.The commercial pilot stated that the purpose of the flight was to apply chemicals to the adjacent fields. After applying four loads of chemical that night, the pilot was returning back to the landing pad that was situated on top of a box truck where he could reload. While attempting to maneuver the helicopter onto the center of the truck's pad, the right skid became caught on an access hole (where ground personnel refill the load). The pilot was unaware of the problem and attempted to reposition the helicopter by lifting the right skid. The helicopter dynamically rolled over off the right rear of the truck and collided with terrain. The pilot sustained injuries as a result of the accident sequence. He stated that there were no preimpact mechanical malfunctions or failures that would have precluded normal operation.