I'm surprised I haven't seen this statistic discussed by the punditry: since Portland joined MLS in 2011, Cascadia - Portland and Seattle to be clear - have been in the Western Conference Finals 7 out of 8 times:
2012: Seattle vs. LA Galaxy
2013: Portland vs. Real Salt Lake
2014: Seattle vs. LA Galaxy
2015: Portland vs. FC Dallas
2016: Seattle vs. Colorado Rapids
2017: Seattle vs. Houston Dynamo
2018: Portland vs. Sporting Kansas City
And here are a couple stats just in case you feel bad that Seattle has been one more time than we have:
Timbers MLS Playoff Record: 7-4-4 (1.67ppg)
Sounders MLS Playoff Record:15-7-12 (1.53ppg)
Conference Final %s: Portland (75%) Seattle (40%)
MLS Cup %s: Portland (25% - if we beat SKC it'll be 50%) Seattle (20%)
And because my two largest investors are both Seattle based (and because I work in Finance): statistics are a hell of a drug. Aside from Seattle's playoff record, there isn't a stat here that has a large enough sample size.
Either way, let's all take a moment and appreciate that there are 12 teams in the West (8 in 2011), and two teams from Cascadia have absolutely dominated the Western Conference in that time (according to my selective statisticking).