The denser and earlier - developed west side nudges up against the nearby West Hills ( Tualatin Mountains ) , while the flatter east side fans out for roughly 180 blocks until it meets the suburb of Gresham .
The denser and earlier - developed west side is mostly hemmed in by the nearby West Hills ( Tualatin Mountains ) , though it extends over them to the border with Washington County . 
 The flatter east side fans out for about 180 blocks , until it meets the suburb of Gresham .