How did I choose the Era, that is to say the setting in time, that my layout would display?

From WordNet:

(n) era, epoch (a period marked by distinctive character or reckoned from a fixed point or event)

My druthers and what these druthers implied in terms of era:

I love large passenger trains.
Well, my layout’s too small for that so this will have to wait for a bigger layout…

I love funky small freight trains.
Any era will do for this…

I want steam locomotives but first generation diesels would be nice.
So we’re talking late 1930s through the 1940s

I want to model the period before the main San Francisco Bay bridges were built.
So pre 1939.

I love steam era maintenance of way equipment.
1910’s to 1940’s

I want my layout to be set during Prohibition.
1920 to 1933

I do not want to model The Depression
Before 1929.

I want to freelance model the Northwestern Pacific Railroad during its peak years.
NWP’s peak year is generally considered to be 1927
NWP had mainly 4-6-0s and 4-4-0s

I’m freelancing a bit which means “I want room to take artistic license.” Therefore I was never going to choose “August 12, 1939” or any other excruciatingly narrow date range.

The era that met the most of my druthers was: the Roaring Twenties. Leaning more towards the late 20s than the early 20s.

What price am I paying?

Looking at my list above I’m going to not have the following:
Large passenger trains
First generation diesels

But I get all my other requirements. I’m okay with this compromise.

Additionally, I am SO fortunate that Bachmann is manufacturing such beautiful 4-6-0s lately and they have just released a perfect 4-4-0.