. ▁James ▁Hall ▁became ▁interested ▁in ▁North ▁Dak ota ▁pale ont ology ▁as ▁a ▁result ▁of ▁Evans ▁and ▁Le id y ' s ▁research . ▁Hall ▁sent ▁Hay den ▁and ▁Me ek ▁into ▁the ▁area . ▁The ▁expedition ▁was ▁a ▁great ▁success , ▁with ▁Hay den ▁and ▁Me ek ▁" collect ed ▁an ▁enorm ous ▁quantity ▁of ▁foss ils ." ▁Hall ▁and ▁Me ek ▁formally ▁described ▁their ▁non - m amm al ian ▁discover ies , ▁while ▁Le id y ▁described ▁their ▁m amm als . ▁ ▁In ▁ 1 8 8 3 ▁Edward ▁Dr ink er ▁C ope ▁made ▁his ▁first ▁for ays ▁into ▁North ▁Dak ota . ▁Among ▁his ▁early ▁accomplish ments ▁included ▁the ▁description ▁of ▁two ▁new ▁kinds ▁of ▁fish ▁from ▁the ▁White ▁River ▁Form ation . ▁The ▁site ▁of ▁C ope ' s ▁discovery ▁attract ed ▁so ▁much ▁attention ▁that ▁all ▁of ▁its ▁foss ils ▁had ▁been ▁collected ▁and ▁the ▁site ▁was ▁" comple t ely ▁m ined ▁out ." ▁In ▁ 1 9 0 5 ▁Earl ▁Doug lass ▁wrote ▁extens ively ▁on ▁beh alf ▁of ▁the ▁Car neg ie ▁the ▁foss ils ▁of ▁the ▁region ▁near ▁C ope ' s ▁work . ▁In ▁the ▁summer ▁of ▁ 1 9 6 3 , ▁Charles ▁I . ▁F ry e ▁discovered ▁a ▁spec imen ▁of ▁Tr ic er at ops ▁in ▁the ▁Hell ▁Creek ▁Form ation ▁of ▁Slo pe ▁County ▁near ▁the ▁town ▁of ▁Mar mar th . ▁It ▁was ▁regarded ▁as ▁the ▁best ▁Tr ic er at ops ▁ske