|Richard Needham. Ski. Fifty Years in North America. Harry N. Abrams, Inc., 1987.
Steve Bradley had been chairman of the National Ski Patrol, with a special interest in avalanche control. When he assumed management of the Winter Park Resort in Colorado in 1950, he joined forces with Ed Taylor to develop a method for smoothing the snow surface. Moguls were a particular problem, traditionally dealt with by teams of men armed with nothing but shovels. Bradley and Taylor's first idea was to ski down the slopes pulling a six-foot length of chain-link fencing. In 1951, they developed the Bradley XPG-1 (Experimental Packer-Grader) which combined a "slat roller" to both pack and powder the snow, in front of which was an adjustable steel blade for cutting off the tops of moguls. The device weight 700 pounds, steered downhill by a skier with his skis wedged in a snowplow. Skiers who performed such work were paid an additional 25 cents per hour "combat pay." At the bottom of the slope, the machines and their operators were taken back up the slope by a T-bar.
Bradley filed a patent in 1951, which was granted in 1957. However, by 1952 the new Kristi and Tucker Sno-Cats were being used to pull the packer-graders.
(Information above summarized from Skiing History.)