  We study the geometry of forces in some simple models for granular stackings.
The information contained in geometry is complementary to that in the
distribution of forces in a single inter-particle contact, which is more widely
studied. We present a method which focuses on the fractal nature of the force
network and find good evidence of scale invariance. The method enables us to
distinguish universality classes characterized by critical exponents. Our
approach can be applied to force networks in other athermal jammed systems.
