ment ▁of ▁the ▁contract . ▁ ▁The ▁Y ellow stone ▁expedition ▁was ▁led ▁by ▁Colonel ▁( l ater ▁General ) ▁Henry ▁At kin son , ▁commander ▁of ▁the ▁ 6 th ▁Infantry , ▁then ▁station ed ▁at ▁Pl att s burgh , ▁New ▁York ▁on ▁the ▁U . S . – Can ada ▁border . ▁In ▁the ▁fall ▁of ▁ 1 8 1 8 , ▁he ▁received ▁orders ▁to ▁rende z vous ▁his ▁troops ▁to ▁the ▁south ▁and ▁enc amp ▁with ▁the ▁crack ▁R if le ▁Regiment ▁by ▁the ▁Missouri ▁River ▁near ▁St . ▁Louis . ▁The ▁ 6 th ▁Infantry ▁hast ily ▁tra ve led ▁the ▁ 2 , 7 0 0 ▁miles ▁by ▁land ▁and ▁water ▁to ▁the ▁area . ▁ ▁The ▁expedition ▁was ▁also ▁char tered ▁to ▁perform ▁science ▁and ▁engineering ▁functions , ▁in ▁conj unction ▁with ▁which ▁a ▁U . S . ▁Army ▁top ographical ▁engineer , ▁Major ▁Stephen ▁Harr iman ▁Long , ▁was ▁ordered ▁to ▁select ▁and ▁lead ▁a ▁crew ▁of ▁notable ▁special ists ▁in ▁zo ology , ▁ge ology , ▁cart ography , ▁journal ism , ▁art ▁and ▁bot any ▁to ▁accomp any ▁the ▁expedition . ▁It ▁was ▁the ▁first ▁scientific ▁expedition ▁of ▁U . S . ▁government - fund ed ▁" Ar my ▁Engine ers " ▁charged ▁with ▁mapping , ▁studying , ▁document ing ▁and ▁expl oring ▁the ▁vast ▁area ▁of ▁un chart ed ▁land ▁between ▁the ▁Mississippi ▁River ▁and ▁the ▁Rock y ▁Mountains . ▁ ▁Ste am bo at ▁Western ▁Engine er ▁Major ▁Long ▁immediately