when I first hit this site there were 2 tables that somehow disappeared but basically under title 10 the president directs you where you will serve. Under title 32 the governor can activate you but only in your state. Also
Natural disasters, such as Hurricane Sandy, raise questions concerning the Presidents legal
authority to send active duty military forces into a disaster area and the permissible functions the
military can perform to protect life and property and maintain order. The Stafford Act authorizes
the use of the military for disaster relief operations at the request of the state governor, but it does
not authorize the use of the military to perform law enforcement functions, which is ordinarily
prohibited by the Posse Comitatus Act. However, the President may invoke other authorities to
use federal troops to aid in the execution of the law, including the Insurrection Act. This report
summarizes the possible constitutional and statutory authorities and constraints relevant to the use
of armed forces, including National Guard units in federal service, to provide assistance to states
when a natural disaster impedes the operation of state and local police.
Unless the President authorizes Posse Comitatus applies:
https://fas.org/sgp/crs/natsec/RS22266.pdf