There are a few West area playgroups off of meetup.com. Here are some links:
http://moms.meetup.com/2597/
http://moms.meetup.com/1568/
There are other ones that are centered in Portland, but have playgroups in the surrounding areas. You can look those up on meetup.com as well. We live in Hillsboro, and have met a lot of moms through those groups. I am also part of a yahoo group that supports babywearing. The main website for all the local groups is www.nwbabywearers.org. Our group is Slingbabes. We have meetings here on the west side.
Welcome to the area! My husband and I moved up here a few years ago (me from CA, him from AZ), and we LOVE it. We love it the most in the spring and summer, though. So many things to do! Feel free to contact me if you would like to hang out, or if you need advice on good places to go with kids. :)
Peace,
E.