Geography help (for world building)

Hobby work, not homework.

I’m world building, how ever I am not a geography guru (so please forgive me for any blatant errors or stupidities). I’m trying to severely isolate this tribe. I want them to have moved (back in pre-history) from a plain to a valley between two mountain ranges and then been closed in by something. I was thinking a canyon, but I have no idea how long it takes for canyons to form or if that’s even feasible (aren’t canyons a desert thing?). Maybe a cliff formed instead? Help me out. It’s a relatively lush area, full of forests. I had the idea that in spring time there’s a lot of temporary streams.

For that matter, how small of an area can I make this? They’re hunters and occasionally farmers (no domesticated animals). I figured they can clamber up the mountains or down the canyon / cliff to hunt and fish or otherwise take long trips to gather food.

Without a lot of time to flesh out an answer, and as a guide to further discussion in this thread, I suggest having a look at the gegography of Papua New Guinea.

Many tribes there were historically isolated in mountain valleys. Even tribes separated by a dozen miles (as the crow flies) spoke in languages unintelligible to one another.

Earthquakes and volcanoes can reshape terrain quite dramatically.

I forgot about Papau New Guinea. Now, can I find some maps of it…

Quartz, do you have some specific examples? I can’t visualize how to make that work.

For volcanoes, there are the Mexican ones - field one day, great honking volcano a year later - and then there’s the Deccan Traps. Nothing seals in a valley like having to cross a sea of lava.

An earthquake might shatter a mountain, causing a huge pile of rubble to seal the valley. Or it might cause land to shift upwards or downwards. Or it might open a gap through which the sea can flow (q.v. the Mediterranean). The sea can then evaporate leaving a vast and impassable salt flat. Or you can reverse it: think of the Great Rift Valley. Huge rift walls on either side, with the habitable area in the middle, the rift stretched every so often by earthquakes.

What you describe sounds like a hanging valley.

You’d need a year-round supply of fresh water, a big enough area for game to be harvested and have it replenish itself, a spot to grow some tubers, perhaps.

You could have a scenario where the tribe lives in the valley and the route they use to make their way up and down the cliff was suddenly destroyed by a landslide.

I suppose a glacier could seal off the entrance to a valley - in extreme conditions they can form reasonably quickly, but you’re still talking decades, probably, for anything substantial.

If an earthquake lowered the valley entrance by several feet, it could easily become a swamp if rivers backed up and couldn’t flow as before. Depending on all sorts od other factors, I could see it becoming a bit impassable at least!
Especially if man-eating crocodiles just happened to move in! :wink:

Whoa. Those look COOL.

Tubers are actually against their religion (seriously - they won’t eat any plant that they have to kill to harvest), but that’s the basic concept.

Thanks everybody!

Ngorongoro Crater is a volcano caldera with pretty tall and steep walls that is a self-contained ecosystem. It’s damn spectacular, although probably not what you are looking for.