A giant crater...means coastline should follow a circle concentric with the ring of mountains...hm, I guess it kind of does that. Sweet. I like it!

So the NW corner is much higher elevation than the rest of the northern coastline? Maybe you could pick that up visually in some way. Like, a little bit of obvious relief on the coast such that it looks a little more obviously like a tilted plateau. I figured that was what was going on there because of the river, but it'd be nice to see it more clearly. The convergent margin on the west coast needs no explanation, though you could probably make the mountain range a little bit wider and more Southern-Andes-like if you wanted to.