The Cat D6C has probably been one of the all time favorites for an intermediate sized dozer. The model shown here is a mid 1970's model equipped for logging. Indeed the photo shown here was taken in 1977. The integral arch on the back of the machine is raised above the winch to provide extra lift for the logs while at the same time guiding the cable onto the winch so it doesn't burn on the edge of the drum if one pulls a load to one side.
Logs hang up on fewer things, and pull easier if they are partially lifted from the ground.
Viewed here it is perhaps difficult to see why the attachment over the winch his called an arch, but the name comes from and earlier tradition of logging arches. For many years, loggers lived and suffered with a trailer mounted arch which was a wishbone shaped structure with the fairlead on top for lift and wheels on the legs. This allowed the front of the logs to hang under the fairlead. This sort of a trailer mounted arch allowed one to move larger logs with a smaller dozer. In recent years direct mounted arches have been almost universally used instead of the trailer mounted ones.