CNN  —  May and early June have always been popular times to visit the Zhangjiajie Forest Park in southwestern China’s Hunan province, before the oppressive summer heat sweeps in. The stunning area is famed for its massive quartz-sandstone pillar formations, which are said to have inspired the floating scenery that appears in the 2009 Hollywood blockbuster “Avatar.” But this year, as crowds of tourists pour into the area, just a few dozen miles away a government-ordered mass cleanup operation