, ▁non - g overn ment al ▁organizations , ▁and ▁academic ▁research ers ▁as ▁a ▁basis ▁for ▁risk ▁analysis , ▁resource ▁management , ▁and ▁environmental ▁study ▁of ▁the ▁continent ' s ▁e cos ystem s . ▁E cor eg ions ▁may ▁be ▁identified ▁by ▁similar ities ▁in ▁ge ology , ▁phys i ography , ▁veget ation , ▁climate , ▁so ils , ▁land ▁use , ▁wild life ▁distributions , ▁and ▁hydro log y . ▁ ▁The ▁classification ▁system ▁has ▁four ▁levels . ▁Level s ▁I , ▁III , ▁and ▁IV ▁are ▁shown ▁on ▁this ▁list . ▁Level ▁I ▁div ides ▁North ▁America ▁into ▁ 1 5 ▁e cor eg ions ; ▁of ▁these , ▁ 3 ▁are ▁present ▁in ▁Oregon . ▁Level ▁III ▁sub div ides ▁the ▁continent ▁into ▁ 1 8 2 ▁e cor eg ions ; ▁of ▁these , ▁ 9 ▁lay ▁partly ▁within ▁Oregon ' s ▁borders . ▁Level ▁IV ▁is ▁a ▁further ▁sub div ision ▁of ▁Level ▁III ▁e cor eg ions . ▁There ▁are ▁ 6 5 ▁Level ▁IV ▁e cor eg ions ▁in ▁Oregon , ▁many ▁of ▁which ▁continue ▁into ▁adjacent ▁areas ▁in ▁the ▁neighbor ing ▁states ▁of ▁Washington , ▁Id aho , ▁Nev ada , ▁and ▁California . ▁The ▁task ▁of ▁defining ▁and ▁mapping ▁these ▁e cor eg ions ▁was ▁carried ▁out ▁by ▁the ▁Oregon ▁E cor eg ion ▁Project , ▁a ▁collabor ative ▁effort ▁involving ▁the ▁E PA , ▁the ▁United ▁States ▁Ge ological ▁Survey ▁( US GS ), ▁the ▁United ▁States ▁Forest ▁Service ▁(