▁Online ▁Books ▁Page ▁▁ ▁( full text ) ▁▁ ▁( full text ) ▁ ▁Category : English - language ▁en cyc loped ias ▁Category : American ▁en cyc loped ias ▁Category : 1 9 0 2 ▁non - f iction ▁books ▁Category : 2 0 th - century ▁en cyc loped ias <0x0A> </s> ▁F oss il ▁Cy c ad ▁National ▁Monument ▁was ▁a ▁national ▁monument ▁in ▁the ▁U . S . ▁state ▁of ▁South ▁Dak ota ▁beginning ▁in ▁ 1 9 2 2 . ▁The ▁site ▁contained ▁hundreds ▁of ▁foss il ▁cy c ads , ▁one ▁of ▁the ▁world ' s ▁greatest ▁concentr ations . ▁Because ▁v and als ▁st ole ▁or ▁destroyed ▁all ▁of ▁the ▁visible ▁foss ils , ▁it ▁was ▁with dra wn ▁as ▁a ▁national ▁monument ▁in ▁ 1 9 5 7 . ▁It ▁is ▁located ▁in ▁north western ▁Fall ▁River ▁County , ▁on ▁U . S . ▁Route ▁ 1 8 , ▁n ortheast ▁of ▁the ▁city ▁of ▁Ed gem ont . ▁ ▁Disc overy ▁ ▁The ▁foss il ized ▁cy c ad ▁b eds ▁were ▁discovered ▁in ▁ 1 8 9 2 ▁by ▁F . ▁H . ▁Cole ▁of ▁Hot ▁Spr ings , ▁South ▁Dak ota , ▁in ▁the ▁ 1 2 0 - mill ion - year - old ▁ ▁Dak ota ▁Sand stone ▁Form ation , ▁near ▁Min ne ka ht a . ▁Cole ▁sent ▁photograph s ▁of ▁the ▁foss ils ▁to ▁Professor ▁Henry ▁Newton , ▁a ▁ge ologist ▁at ▁the ▁Smith son ian ▁Institution