While the USA was once a true federation of sovereign states that really hasn't been the case since at least the Civil War, over 150 years ago. States depend heavily on the federal government for assistance, standardization, and regulation, and even depend on their neighbors for logistical support in various industries as well as energy and water.

For all its touted net-contribution to the federal budget California would not survive on its own, as it depends on electricity from other states and water from the Colorado River (a shared resource between several states). To be sure, California puts these shared resources to extremely productive use and pays back the value to its neighbors, but this kind of interdependence probably would not exist if California went rebel.