Does your mod (or do you know of any other cave mods) allow both resources at the surface level AND underground?
Regards,
~B

I started a discussion on that here, this mod does not currently support it: https://mods.factorio.com/mods/CaveGrinder/Caves/discussion/17210

There is a bit of technical discussion about multiple features in that thread tho, might be good to break it out here

There are other mods that allow multiple "surfaces" with resources, but I haven't seen any that provide a cave-like experience

yes might be easier to have a thread for only this here
Currently not yet, but i want to add this.
I was struggling a bit with how to do the settings, since i wanted a nice dialog (e.g. dropdown/checkbox per existing resource) but that seemed to be impossible in a generic way. (no access to the global state at that point)
so i am considering an approach quite similar to bitbased's patch; one string to specify which resources are excluded from the transfer into the cave.

This is the format of the string I ended up with for "List of surface resource names":

Basic usage for specifying which resources should be only on the surface:
all -- all resources are surface resources, no cave resources
both -- all resources are both on surface and cave
crude-oil -- crude oil is on the surface but not in the cave
crude-oil stone -- crude oil and stone are on the surface and not in the cave
both coal -- coal is only on surface, but all other resources are both on surface and cave

More advanced usage with + for including a resource both on surface and cave:
+all -- same as "both" above
+stone -- stone is both on surface and in cave, all other resources are only in cave
crude-oil +stone -- stone is both on surface and in cave, crude-oil is only on the surface, all other resources are only in cave
all +coal -- all resources are only on surface, except for coal, which is also in cave

Here are the patched files, and a git diff:
https://www.dropbox.com/s/071b65en9virfwy/SurfaceResourcesPatch.zip?dl=0
https://www.dropbox.com/s/ivi17l66i7ia5zm/SurfaceResourcesPatch.diff?dl=0

thanks for the diff; i have implemented it now into 0.1.6
basically i liked the flexibilty you added here, but thought that for a user it is difficult to specify it like that. so instead i added a dropdown for the default value ("nowhere", "cave-only", "surface-only", "cave and surface"), and then 4 additional string settings where users can name individual resources that should behave differently. the default is that crude-oil is surface only, and stone is both, everything else is cave-only.
i added this now in version 0.1.6.

i investigated the direction of the data-raw-prototypes approach, but finally decided against it. i think it is a quite useful mod but i am not sure how robust it is against future changes, and i don't want to force a dependency on to all users. (an optional dependency doesn't make sense to me here since that makes the code more complex while providing more confusion to users).
also, personally i am not a fan of regular expressions although i see that without a string split function in lua it kind of forces that direction; but for me they are always a mystery; especially when i later have to come back to them for debugging :)

Tnanks, sounds great! ... and yes, regex in Lua being completely different (and less powerful) than basically every other languages regex is also "fun" :-D

Sounds awesome! I assume this is something recommended for new game starts only, right?

yes, on an existing save the same settings as before are in effect, and changing the settings after map creation won't take an effect. maybe it should, but i didn't consider that.