▁is ▁the ▁dens ely ▁populated ▁Wei ▁River ▁valley , ▁an ▁ancient ▁center ▁of ▁Chinese ▁civil ization . ▁To ▁the ▁south ▁is ▁the ▁Han ▁River ▁valley . ▁To ▁the ▁west ▁is ▁the ▁line ▁of ▁mountains ▁along ▁the ▁northern ▁edge ▁of ▁the ▁Tib et an ▁Pl ate au . ▁To ▁the ▁east ▁are ▁the ▁lower ▁F uni u ▁and ▁D ab ie ▁Sh an ▁which ▁rise ▁out ▁of ▁the ▁coast al ▁plain . ▁ ▁The ▁northern ▁side ▁of ▁the ▁range ▁is ▁pr one ▁to ▁hot ▁weather , ▁however ▁the ▁physical ▁bar rier ▁of ▁the ▁mountains ▁mean ▁that ▁the ▁land ▁to ▁the ▁North ▁has ▁a ▁semi - ar id ▁climate , ▁with ▁the ▁lack ▁of ▁rich , ▁fert ile ▁landscape ▁that ▁can ▁not ▁support ▁a ▁wealth ▁of ▁wild life . ▁The ▁mountains ▁also ▁acted ▁as ▁a ▁natural ▁defense ▁against ▁nom adic ▁invas ions ▁from ▁the ▁North , ▁as ▁only ▁four ▁passes ▁cross ▁the ▁mountains . ▁ ▁In ▁the ▁late ▁ 1 9 9 0 s ▁a ▁railway ▁tunnel ▁and ▁a ▁spir al ▁was ▁completed , ▁thereby ▁eas ing ▁travel ▁across ▁the ▁range . ▁ ▁The ▁highest ▁mountain ▁in ▁the ▁range ▁is ▁Mount ▁Ta ib ai ▁at ▁, ▁which ▁is ▁about ▁ ▁west ▁of ▁the ▁ancient ▁Chinese ▁capital ▁of ▁X i ' an . ▁Three ▁cult ur ally ▁significant ▁pe aks ▁in ▁the ▁range ▁are ▁Mount ▁H ua ▁( ), ▁Mount ▁Li ▁( ), ▁and ▁Mount ▁Ma iji ▁( ). ▁ ▁Environment , ▁fl ora ▁and ▁fa una ▁ ▁The ▁environment ▁of ▁the ▁Q in ▁Mountains ▁is