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OP, any of the major metro areas in the west are going to have what you are looking for. Despite the fact that California cities are known to be expensive (minus Sacramento which is more affordable) people make it work by either downsizing their housing or by commuting a little further. Any of the major CA cities will have tons of social groups for people in their 20s and 30s who love hiking, camping, kayaking, climbing, surfing, etc. etc. both locally, as well as in other parts of the state and beyond into other western states.
Obviously the other usual suspects in the west are great places. Seattle, Portland, Denver-Boulder, etc. Out of these Denver-Boulder is the one I am personally familiar and seem to prefer.
Other smaller big cities in the west that can also be great for meeting people in their 20s and 30s that I have a little knowledge of would include college towns like Tempe, Tucson, Albuquerque. Possibly Reno, NV might even be an idea (closest city to Lake Tahoe), even SLC, Utah is becoming a bit more progressive.
Places that come to mind in the east however would include largely college towns. The larger cities in the east are hard to meet outdoorsy people.
Medium sized areas/cities in the East may work and it may depend on the outdoor activities you want to take part in. Think the bigger Upstate NY, Springfield and Worcester MA, Hartford CT, Winston-Salem and Asheville NC, Upstate SC and the Scranton/Wilkes-Barre, Allentown-Bethlehem-Easton and Harrisburg PA areas.
You're not contributing to answering the question, you are only trying to start something, and furthermore your post is self-evident about the unwelcome, hostile, judgmental ignorance that would give the northern Rockies a bad name (minus places like Jackson/Tetons/Yellowstone, Missoula, Glacier NP).
Don't hate the player, hate the game.
On a more serious note, I'd recommend OP pick a bunch of places and visit each one. Socializing is what one makes of it.