Autonomous zone and seat of a seditious rebellion are two different things. There are plenty of autonomous zones around the country and traditionally the ones which get hit are the ones where some group of people there decide they are going to use it as a forward operating base to conduct takeover operations somewhere. Even Communist China has allowed some autonomous zones. That was the internal diplomatic give-back after the Tienanmen Square thing in 1989. The Communist party of China was not going to give up the whole country, but Deng Xaopeng convinced them to give the people a region to go to, so they had already allowed Hong Kong and Taiwan to function as autonomous zones, and under the British, there was a part of Hong Kong called Kowloon City which was autonomous.

In the 1990s though, the Chinese were looking at giving up a swampy area just accross the straits from Hong Kong, since a lot of illegal trade had been going on there anyway, and a lot of PRC officials had their fingers in it anyway, so that got declared the zone for economic reasons. Go check out the developments on what was to be a Christian refugee camp with relatively free trade economics. That's the Shenzhen area. Check out videos of the area to see what economic success looks like.

In the Arab world, there have been little areas declared not subject to Sharia law. Dubai, kinda Muslim, but they wanted an area technically not in Saudi for whorehouses and discos. That's where the supermodel Australian chicks go to make $1200 a night.

It means you are not doing armed marches on any capitol or using it as a base from which to taunt the government to come and bomb you. Big reasons to make sure the persistently troublesome psych cases are weeded out or straightened out prior to permanent residency.

Nobody is carpet bombing any Indian reservations either.

These things run in stages:

Secret
Known
Tolerated
Defacto
Declared
Officially recognized
Sovereign

Now most private property in the US, on parcels large enough especially in the more sparsely populated areas of the western states you get all the way to somewhere between defacto and declared just by occupying the land legally. Official recognition is only one small step away when you are talking about municipal incorporation.

On municipal incorporation, you look at some of the big cities with strong liberal leanings and how they would regularly thumb their noses at conservative presidential administrations. SanFrancisco, Berkeley. Then you have New York City running its own spy agencies whose capabilities surpass a lot of national governments.

Then there is the defacto situation, like the Mormon Deseret, or Mormon colonies in Mexico. Vice media did an interesting series on that a few years back, related to the Romney family in Northern Mexico. They have had a defacto autonomous zone for over 100 years.

I would say to be on the safe side, for the first decade maybe, your population maintains some mobility. Temporary autonomous zones have their limitations, but can eventually benefit from permanent development. You see that with the snowbird RV people, setting up in parts of the Northwest in the summer, the southwest in the winter, eventually contributing to the infrastructure of the areas they frequent. At first it is just restroom facilities, repair shops and convenience stores, but eventually they become the lifeblood of some of the little towns. Usually supporting a couple RV dealerships, a VA clinic and some retiree services type things.