[x,y,z] = peaks;
surf(x,y,z)
hold on
xl = xlim; yl = ylim;zl = -zlim;
mesh(zeros(size(x))-xl(1),y,z);
mesh(x,zeros(size(y))-yl(1),z);
mesh(x,y,zeros(size(z))-zl(1));
hold off