Why wouldn't my colonists go to see what's going on down there?

I would like my human colonists to settle on the high plateaus (2500-3000m above sea level) of my planet thus never meeting the civilization living in the lowlands (in a huge forest so they aren't visible from above), until settlers find evidence of them and decide to see what's going on down there. The thing is that I need a reason why they wouldn't go to those lowlands earlier, so something that makes the descent difficult but not impossible, and also why my civilization wouldn't develop on the plateau. Here are the main ideas I had:

• Hostile environnement at the edge of the plateau. I don't think it could stop my civilization, humans lives in deserts and very dense rainforests with plenty of deadly animals, nor why wouldn't my colonists just go through it with their technology but if you have any idea how it could work it's ok

• Oxygen levels (or any other gas). This my favourite idea but I'm not sure it would work. It's easy to make my civilized species highly oxygen-needing so they can't live on the platea. For my colonists I know that high pressure of most gases are dangerous but is there any effect that is just very uncomfortable, like the light hypoxia you feel when above 3000m or so?

If you have something that could make the second idea work it's perfect, otherwise just find something that could fix the first or a brand new one.

Background:

My story takes place in the 22nd century. The colonists are mainly scientists who came here to explore and study the planet. There are 50 and they have buggies, guns and an helicopter. A few months before the evidence of alien civilization, all the AI in these are destroyed by a computer virus which came in a message from earth (but it might be an e-mail they didn't open before). The purpose of the virus was to destroy all the AI used on earth and it was send in basic telecommunications from NASA. Now they just have some basic technology like solar panels and everything that didn't have any AI in it. I'm not sure why wouldn't they have pressurized air tanks. Basically they had advanced technology but no incentive to go to the lowlands, then later they have only basic technology but must be able to go in those lowlands, and I'm wondering why they didn't have incentives to do it before.

posted about 6 years ago

Jean-Abdel‭

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