So I have an idea for a campaign seting/country for a (as of now) still none existing D&D campaign i'd like to run.
The basic premise of the idea is that a sizable sea got cut of from the ocean and thus evaporated leaving behind a salt flat desert situated well below the sea level and "mountains" with what used to be islands on top (this actually happened to the Mediterranean sea which is where my inspiration came from).
Today i drew up a sketch of the map with the important features, the thing is i'm having a bit of a hard time figuring out the geology of it all.
2016-04-25 18.19.16.jpg
now for the legend:
light blue= fresh water - dark blue= salt water - thick lines indicate cliffs (think Mount Roraima) - and the strip of ogre yellow down there is a massive sand slope leading to the neighboring (sand) desert (i refer to it as "the beach") - mountains are triangles and green is plants but you got that far already i'd bet.

I have so many questions:
what kind of climate would this area be now that an entire sea is no longer there?
how do mountain ranges behave?
how much would the cliffs slope if at all ?
what happens to coral reefs if the sea they're in evaporates ?
How does one properly scale a map like this (the whole basin is pretty damn huge think maybe 2/3 of the Mediterranean sea)

this would probably also be the time to mention that while i have Photoshop,corel painter and a Wacom i am not even remotely proficient with any of them, i'm far more comfortable with "traditional" Mediums (media ??).

In my mind this entire country is "walled in" by massive 400/500 meter high cliffs except for at the bottom where "the beatch" and the top right corner where a mountain range comes down into the basin but how plausible is that ?
pfffff so many questions i can feel myself getting lost in it all.

I eagerly await your sagely advice o wise ones.