Is a river canyon realistic here? Why or why not?

[eepjr24]

If you look at the Sierra Nevada mountains in California, that's an example of a large batholith that's being pushed up as part of a collision with the North American continent. There are a lot of other things going on in that area and it's hard to get things like that happening in isolation. Note that Yellowstone is a special case as it is a hotspot burning through the crust (see the Snake River Plain for an example of what it did on the way to where it is now).

I said Yellowstone, but what I was really thinking of was more like Arenal in Costa Rica. Hot rivers that get into the 110 degree range in spots, natural bath pools, etc. This would be from volcanic activity deep inside the mountain. Not looking for active geysers, acid pools, lack of plant life, etc.

A large batholith like that would need to be emplaced from something like a previous continental margin. Only much later would something push it to the surface. The fun thing about that sort of behavior is that you can get nice linear features (see the Kern River Canyon in the southern Sierra Nevada mountains in California) caused by breaks in the batholith.

I am afraid you lost me on that. Does that mean I am better off justifying the large mountains with tectonics or volcanic activity?

As far as the valley goes, is your intent to have it get narrower or wider as it heads to the sea?

Honestly, I would love some advice on that. My initial thought was that it would be narrower but deeper near the head and widen somewhat as it slows and gets to the sea? Do these canyons sometimes have large waterfalls at their heads? That makes sense to me, but not sure if it is just wishful thinking.

I will admit to being curious about its significance and whether it needs steep walls and a flat bottom or if a more traditional V shape is as useful?

I would lean more toward the steep walls, but it will likely vary somewhat naturally depending on the material being cut through and the speed of the water at that area, correct? Basically, as long as it is very difficult to traverse terrain that makes you vulnerable to attacks from above it will serve my purposes. Magic will make things a bit more difficult, but those with the ability to move large numbers of troops in this manner will be both rare and targeted.

It will be a contested border between protectorates of two colonial powers in the area. The southern colony has been neglected since the silver and mercury mining has become more difficult (similar to Peru in the 1700's by Spain). The northern colony is more independent and somewhat similar to the US near the time of formation, but pre-Revolution. The rest of the border is either harsh mountain terrain or a very dangerous tropical rainforest on the southwest border. The conflict is more simmering than active at the moment, but that could change depending on the actions of the party(ies) who will be adventuring.

I will post an updated map to my WIP thread tomorrow at some point, my eyes are too tired to try it tonight.

- Ernie