How to shade an area below a set of points?

Hi,

I have a question on shading an area determined by a set of points (blue points on the image) on the interpolated data.

This plot is surf(X,Y,F(X,Y)), where F(X,Y) is my interpolated data. Points in blue are minimum points Xmin and Ymin. I tried using fill(Xmin,Ymin,'b') or area(Ymin) but they don't help.

How should I go about constructing a matrix to be shaded and which command should I use to shade area below the set of points?

Thanks in advance for your help!

Best regards, Sofya