From what I was told by some insurance brokers is that, at least on the west coast, earthquake insurance is offered as a supplemental option and the policies I received costs several hundred a month.  

However, if I decide to buy it, I plan to convert it to natural gas since there is already a gas line into the property (i.e. there's a gas stove in each unit) and natural gas is cheaper for the tenant.

Like oil, timber, some land, minerals, and other natural resources.

Re: the retirement income, currently my income has been good, though I am a frugal person by nature and really don't spend much.

For "gas" as in CNG (Compressed Natural Gas), I disagree.

You won't see the appreciation in these areas continue very long because wage rates for the hourly folks are not following the same upward path and that will naturally keep the balance. 

I was planning on buying raw land, and it seemed like you could make a killing by layering over several different uses, including leasing hunting rights and pumping oil and natural gas, or timbering the land.When I crunched the numbers, they always seemed to work out.

Currently there is a non-conforming bedroom along with a total of  1,000sqft of livable fully  finished and well lit from natural light living space, including a bathroom and laundry — and a kitchenette area.  

The natural appreciation has been strong enough that we are still holding this property.Lessons learned?

I am risk adverse by nature but enjoy doing calculations and thus taking calculated risk thus here I am now.