Simplify the following text for a Grade 14 native English-speaking person.
Original: It originally included all of the present-day states of Idaho , Oregon and Washington , as well as Montana west of the Continental Divide , and Wyoming west of the Continental Divide and north of the 42nd parallel northâ '' the northern border of the Mexican Cession .
Simplified: The Territory of Oregon originally encompassed all of the present-day states of Idaho , Oregon and Washington , as well as those parts of present day Montana and Wyoming west of the Continental Divide .