- Planet colonized, several generations passed, knowledge of tech & being a colony is gone
- Robot guardian has been trying to help by giving the tribe replacement tech
- Culture has "taboo" around many things, including ascending a nearby mountain (discovered by the main character to be a result of altitude sickness)
- There's a... rising river?
- Some of the original colonists (or their children?) who know the history are still alive, but are seen as senile & not taken seriously
I read this probably in the late 80s or early 90s when I was young - I'm not sure if it's young adult or not, and I don't remember if it was a short story, novella, or full length.
It follows a character - a young person (?) in a primitive-ish "tribe," who is interested in exploring the world. She knows she's not supposed to go up the mountain, because it's taboo. (Many things are, which she's frustrated by).
She does eventually do so anyway, and gets sick. She's been taught that ill would befall her for violating the taboos of her culture, but, at some point, she has the line "is the sickness because of the taboo, or is the taboo because of the sickness?"
I believe she is rescued by a robot guardian at some point. He takes her to a cache in a cave, with a computer and such. He's been giving the tribe various things to replace broken components, such as a flourescent light tube, a replacement microchip, and surveying rods, because there's a river rising or such.
Back at her tribe, with the striped rod, an elder says "that looks like one of the surveying rods we used when we came here!" But, everyone considers these elders - probably the original colonizers - to be senile, and they don't take them seriously.
Sorry about the rambling nature of this!