3d block model to 2d surface layer

I have a set of x,y,z points (csv) with attributes. This is a three-dimensional geologic model - I'm essentially trying to isolate the points on the surface, that is, those with the largest elevation value.

So, I have multiple points with the same X,Y values. From features with identical X,Y values, I want to select the one with the largest Z value.

Any suggestions?