We did not own the cabin last year so we don't have rental property income to show historic values.

Of course Southern California has had high appreciation historically over the long term and especially the past several years ...but there have also been big dips too. 

That can be lot size, topography, other physical characteristics, lot shape, biological considerations (such as a historic tree on the property), etc. 

With mortgage rates near historical lows, seems to me like locking in a long-term fixed rate is the wise thing to do.

Theoretically and historically, M2 is directly correlated with real estate price.Would there be another dramatic jump in housing price in the next few years?

Interest rates hovering in the 6%-7% range are higher than you’ve come to expect from the past decade, but they’re not outrageous (or even considered that high) from a broader historical perspective.

If historical rental data is unavailable, you can use the rate of appreciation in the area as a proxy, as rents tend to follow prices.

6% is historically low, who's to say rates will ever go lower (though I think they'll have to)?   

So if you plan to own and hold for 4 years, based on historical data, it seems like it could work out for you.

Prices don't always go up and I believe historical rates have averaged around 6-8%.