Late 60s or 70s movie... set on either contemporary decade... conspiracy, action, thriller... either American or Canadian... most likely American... there's a scene where a whole bunch of men are holed up in a wealthy ranch stronghold somewhere in a desert in what seems the American midwest... and on the last scene, or nearly last scene, a whole bunch of armed men in overalls walk out of an elevator in an office building and shoot everyone in one of the floors...