The foothills of the Blue Mountains start about 30 miles west of Sydney. Consisting mainly of sandstone, they are dissected by dramatic gorges up to 2,500 feet deep. Since 2000, the Greater Blue Mountains Area has been listed as a UNESCO World Heritage site. The predominant vegetation is eucalyptus forest, though sheltered areas contain temperate rainforest. Each winter, the higher elevations receive light dustings of snow. The name of the range stems from the curious fact that as temperatures rise, eucalyptus oil evaporates, which has the effect of exaggerating the blue end of the spectrum.