An Oasis is like a walled city state. They're a mix of futuristic and ancient- Think, india-like. Stereotypical india but with a lot more tech and green and way less suffering. They sprung up out of nowhere when they arrived, veering away from cities and areas with extreme levels of pollution. There however is at least 1 or 2 per region, sometimes per country if they're big enough.

Animals inside have not evolved, but outside I assume they have. Just enough to survive on

The nearest camp from the Oasis we start at is a good 3 hour walk- they're the ballsiest, thinking that patrollers wont look so close. Otherwise, idk.