I left Or-e-gun in 1990 before coming to MT, and then based on my USFS work, been in or immediately next door in ID until 2009 when an assignment took me back east with a permanent return in 2012. When in Idaho I was in & out of western MT on a regularly basis, except for 2002-2003, for work & personal business, so I've seen Western MT change over time.  The last few years the change has occurred faster.

I was last back to OR in 2002 for a training session in Portland, and had an encounter with some feral gang of kids along the river walk. I stared them down and they backed off. I need to go back to OR for a visit next year to see friends I worked & went to school with, and see how much the Willamette Valley's gone down hill.

OR Gov. Tom McCall once said "Don't Californicate Oregon". I think he's revolving in his grave.

Regarding only the west side getting growth, Helena and Bozeman have changed dramatically.  I think any of the "island" cities (my term for the major cities in MT surrounded by all the open country, will see continued growth.

My Wife and I left Oregon in 1989 when I was transferred to Hawaii, I ended up on the other side of the world in Jan 1991 and once that mess was over with, settled back in WA, then left WA in 97 and have lived full time in MT since then.  Last time I was in OR/WA was three years ago when my Dad passed away and have no plans to go back ever again.