Join Overlapping Terrain Surfaces I am trying to create a terrain surface for laser slicing.
I have several publicly available terrain surfaces. The surfaces have some overlapping, but the overlapped faces are not same on both surfaces.

I finally want to have an object similar to below without internal surfaces

I tried to extrude individual surfaces, and join. There are internal surfaces remained.
I tried to extrude individual surfaces, and do boolean operation: Object A union (Object B difference (Object A intersect Object B)). There are still internal surfaces.
Can anyone tell me how to do this?
I tried to cut the overlapped surfaces by bisect tool at a specific coordinate (say at certain $Y$) on both surfaces, then extrude and join. but there are still internal surface.
Finally, here is my solution.

cut one object's edge by bisect tool at position very close to another object, keep a gap between the two objects.
join the two objects into one.
enter edit mode
select the two edges at the sides of the gap
use edge bridge tool.