Before the 1971 race, the course underwent its most significant changes of the Grand Prix era, as it was extended from to by the addition of four corners in a new section called the 'Boot' or 'Anvil'. The new layout departed from the old course near the south end into a curling downhill left-hand turn through the woods. The track followed the edge of the hillside to two consecutive right-hand turns, over an exciting blind crest to a left-hand turn, and back onto the old track. In addition, the circuit was widened and resurfaced, and both the pits and start-finish line were moved back before the northwest right-angle corner known as "The 90" and in 1975, a fast right-left chicane was added in the Esses section to slow speeds through the series of corners.