▁that ▁diver ts ▁the ▁Aw ash ▁River , ▁forming ▁a ▁partial ▁dam ▁and ▁creating ▁Lake ▁Y ardi ; ▁and ▁it ▁contains ▁the ▁Bou ri ▁Form ation . ▁The ▁pen ins ula ▁is ▁about ▁ 4   km ▁wide ▁by ▁ 1 0   km ▁long , ▁and ▁lies ▁in ▁a ▁N N W - S SE ▁direction ▁in ▁the ▁Qu atern ary - period ▁r ift ▁zone ▁in ▁the ▁southern ▁part ▁of ▁the ▁Af ar ▁De pression ▁( A far ▁Tri angle ). ▁ ▁The ▁Bou ri ▁Form ation ▁is ▁a ▁sed iment ▁area ▁some ▁ 8 0 ▁m ▁thick ▁that ▁st ret ches ▁down ▁much ▁of ▁the ▁length ▁and ▁breath ▁of ▁the ▁pen ins ula . ▁The ▁formation ▁consists ▁of ▁three ▁ge ological ▁units , ▁called ▁members , ▁from ▁which ▁foss ils ▁and ▁artifact s ▁of ▁different ▁periods ▁of ▁human ▁evolution ▁have ▁been ▁exc av ated . ▁They ▁are : ▁the ▁lowest ▁member , ▁named ▁Hat ay ae , ▁or ▁the ▁H ata , ▁dated ▁to ▁ 2 . 5 ▁million ▁years ▁ago ▁( my a ) — and ▁in ▁which ▁foss ils ▁of ▁Austral op it he cus ▁gar hi ▁were ▁found ; ▁the ▁Dak ani hy lo , ▁or ▁D aka , ▁member , ▁one ▁( 1 ) ▁my a — f oss ils ▁of ▁H omo ▁ere ct us ▁were ▁found ; ▁and ▁the ▁Her to ▁member , ▁Lower ▁layer ▁at ▁ 2 6 0 ▁k ya , ▁and ▁Upper ▁layers ▁at ▁ 1 6 0 ▁to ▁ 1