Speculation: How long would it have taken....

[Cabbage Patch]

...Given the location of Irwin and the time that had elapsed (about 3 months since Zday when Michael & crew arrived and then 5 more months before Red Winter), was it a foregone conclusion that the Zeds would have gotten there eventually? Or not?

One of the factors I've always considered key to the survival of Fort Irwin up to this point is its isolation. The main base is 45 miles up a secondary road from the nearest town. The only ways I'd expect a Z to find it is if it followed someone there, which appears to have been what happened in the end. I suspect that Irwin had stood up to many minor incursions by Zs up to the point of Red Winter, and that it could have held out just fine if it hadn't been for the combination of the Little Ones and the Boulder refugees.

...The question popped in my head thinking about some out of the way places in this country that aren't near the big cities at all. How many of them are basically Zed free at this point in the story? Or is Irwin/Boulder an anomaly in the WA universe?

I've been wondering what made Boulder special. Yes, it's a little off the beaten track, but it's still serviced by freeways and it's not that far from the Greater Denver metro area. I suspect that if Boulder, and Fort Irwin, and the Colony could hold out that there should be other isolated pockets of humans surviving elsewhere in the country.