▁the ▁West ▁and ▁North ▁of ▁China ▁where ▁there ▁is ▁less ▁ra inf all ▁than ▁the ▁main ▁kar st ▁region ▁in ▁the ▁S out heast . ▁China ' s ▁kar st ▁regions ▁are ▁almost ▁all ▁formed ▁in ▁rocks ▁of ▁Dev onian ▁to ▁Tri ass ic ▁age . ▁Near ▁Gu il in ▁the ▁lower ing ▁of ▁the ▁base ▁level , ▁through ▁u pl ift ▁and ▁river ▁er os ion , ▁has ▁formed ▁prominent ▁kar st ▁hills . ▁It ▁is ▁estimated ▁that ▁the ▁river ▁er odes ▁down ▁ 5 0 – 1 0 0   mm / ky r , ▁from ▁this ▁the ▁age ▁of ▁the ▁kar st ▁landscape ▁is ▁estimated ▁at ▁ 1 0 – 2 0 ▁million ▁years ▁( M i oc ene ). ▁ ▁Des ert ification ▁and ▁lo ess ▁ ▁The ▁central ▁China ▁lo ess ▁sequence ▁records ▁many ▁periods ▁of ▁clim atic ▁variation . ▁During ▁dry ▁( o ften ▁cool er ) ▁periods ▁wind ▁er os ion ▁increases ▁and ▁lo ess ▁is ▁depos ited , ▁while ▁during ▁wet ter ▁and ▁war mer ▁periods ▁pale os ols ▁form . ▁The ▁desert ification ▁of ▁China ' s ▁interior ▁is ▁infer red ▁to ▁have ▁started ▁ 2 3 ▁million ▁years ▁ago ▁( E ar ly ▁Mi oc ene ) ▁due ▁to ▁the ▁formation ▁of ▁lo ess ▁depos its ▁from ▁this ▁time ▁until ▁ 6 . 2 ▁million ▁years ▁ago . ▁ ▁The ▁gla cial ▁and ▁inter - g la cial ▁Ple ist oc ene ▁clim atic ▁cycles ▁are ▁also ▁presented ▁in ▁the ▁lo ess ▁depos