▁ 6 4 5 , ▁during ▁the ▁As uka ▁period , ▁the ▁hill ▁range ▁became ▁part ▁of ▁three ▁provinces , ▁Sh im ō sa ▁Province ▁to ▁the ▁north , ▁Kaz usa ▁Province ▁in ▁the ▁middle ▁part ▁of ▁the ▁range , ▁and ▁A wa ▁Province ▁to ▁the ▁south . ▁The ▁hill ▁range ▁is ▁noted ▁for ▁its ▁rich ness ▁of ▁cast les ▁built ▁during ▁the ▁S eng oku ▁period ▁as ▁part ▁of ▁medieval ▁conflicts . ▁ ▁Modern ▁history ▁▁ ▁The ▁provinces ▁end ured ▁until ▁Ch iba ▁Pref ect ure ▁was ▁established ▁at ▁the ▁end ▁of ▁the ▁ 1 9 th ▁century ▁in ▁the ▁Me iji ▁period . ▁The ▁B ō s ō ▁Hill ▁Range ▁provided ▁a ▁natural ▁fort ification ▁against ▁air ▁attack ▁of ▁Tokyo ▁during ▁World ▁War ▁II , ▁when ▁the ▁ 2 5 2 ▁Air ▁Group ▁of ▁the ▁Imperial ▁Japanese ▁Navy ▁( I J N ) ▁built ▁the ▁M ob ara ▁Air ▁Field ▁in ▁ 1 9 4 1 ▁in ▁M ob ara . ▁After ▁the ▁war ▁land ▁reform ▁was ▁carried ▁out ▁in ▁the ▁region . ▁The ▁eastern ▁part ▁of ▁the ▁hill ▁range ▁saw ▁major ▁economic ▁development ▁as ▁part ▁of ▁the ▁greater ▁Metropolitan ▁Tokyo ▁region . ▁ ▁Econom y ▁▁ ▁The ▁hill ▁range ▁was ▁known ▁for ▁char co al ▁production ▁in ▁the ▁past . ▁The ▁hill ▁range ▁is ▁still ▁home ▁to ▁many ▁da iry ▁far ms . ▁N umer ous ▁golf ▁courses ▁were ▁developed ▁in ▁the ▁hill ▁region , ▁and ▁recre ational ▁facilities ▁continue ▁to ▁be ▁developed ▁in ▁the ▁area . ▁The ▁hill ▁range