No idea, but I'll be very interested in the responses!

A community is made up of lots of great people with different ideas and they aren't all necessarily "liberal" whatever that means.

Am I correct in assuming this has to be IN California and nowhere else?

What do you mean by "active?"

Can this be an actual spread out physically community or does it have to be in a particular building as say a condo?

Active is usually a word for younger demographics, but in this sense, I wonder if you mean politically activist (ie, bus trips to protest some places as a feature of the community?).

I'd think the best bet is a place located in an area known for that type of population, San Luis Obispo sounds a likely bet, but so would San Francisco. I'd also think you'd have to find something like that in Portland and Eugene, OR and San Mateo in CA (and of course, Berkeley, but not sure there are retirement communities there). I used to live in Santa Monica, it's liberal and progressive enough, but very expensive. I had friends in San Luis Obispo and I can imagine that such a thing exists there.

I guess you should specify if you are just using the word community in the sense of a town/location, or do you mean a particular housing development or apartment building.

The problem with a lot of cities (like where i live, Washington DC) is that in a large urban area, you couldn't predict which people would go to live in a certain place as both liberals and conservatives live in the area.

You might want to consider Claremont, CA.

If you want old (& young) retired liberals full of political action, come
see us in Ashland, Oregon.

http://www.ashlandchamber.com/Page.asp?NavID=825

Whoops! Meant to add this:
http://bestboomertowns.com/towns/ashland_oregon/

When I think of liberal and diversity I think of the San Francisco area.

Then again Portland, Oregon would be perfect for all kinds of outdoor activities (skiing, biking, kayaking, jogging, etc). And Portland is one of the most liberal cities I've been too (my DD and SIL live there so I visit fairly often).

They are very progressive when it comes to environmental practices, politics, food (organic, local, in season, and is considered the Paris of the USA).

Davis, California would fit the bill.

Oxymoron?

Canada

Crawford Texas? ?

Lots of gobbley-gook answers.

I agree about SLO, it's considered the happiest town in the United States.

I have family that have retired in the area and they love it.

Oxymoron?

Is that near Oxnard?

People in SLO didn't seem any happier to me than anywhere else.

And I've been to Portland and whoever is calling it the Paris of the USA is loony. It isn't remotely close to being like Paris, France in any way I can think of.

Paris of the US, lol, but Christina, I assume nanabee meant with regard to food, specifically access to the best locally produced, seasonal products, and that just might be true.

I wish the OP would say if it really has to be in California. If it does, I would suggest Berkeley, or SF itself.

At present i am living in my own home in Sherman Oaks, CA which is in Southern California. I do not want to maintain a home anymore. Prefer a planned community where i can have a unit with space for vegetable garden,not a city or small town. I am 65 year old female with a lot of good energy. So active means being with people who are interested in the world and want to participate. That doesn't mean every minute of every day, but, a sincere desire to participate and encourage change. It would also be great if there were book clubs, art classes, discussion groups, hiking groups etc.

i am a warm weather person, so Washington D.C. would be to cold, as would be Portland. For those of you whose entries were sincere, I thank you.

People do seem do like SLO. I'd ask this question on citydata form, starting with the SLO one.

The resources you are looking for exist in college towns. We are in cold New england so weather would not suit, but people retire here due to the cultural opportunities within the five colleges located here.

One concern I would have is that in my experience planned communities with units often do not allow gardening. Perhaps search cohousing communities.

Del Webb communities are really nice - http://www.delwebb.com/retirement-communities/California/Southern-California/default.aspx?ha=0