The brake run you are talking about was originally set up to be a block brake. When it was built, The Beast utilized sked brakes, which took a long distance and need to be kept dry, thus the long shed. This was done so The Beast could run four trains at one time. Unfortunately, the block was too short to run 4 trains practically,and the fourth train was removed. The end result was one long trim brake.
EDIT: SOB_Tom beat me to it, I type too slowly.