resource after the "organized militia" is exhausted that a governor can use "in case of war, rebellion, insurrection, invasion, tumult, riot, breach of the peace, public calamity or catastrophe, or other emergency, or imminent danger thereof".
One example is California, our largest state with nearly 37 million citizens and potential for all sorts of emergencies.
121. The unorganized militia consists of all persons liable to
service in the militia, but not members of the National Guard, the
State Military Reserve, or the Naval Militia.
122. The militia of the State consists of all able-bodied male
citizens and all other able-bodied males who have declared their
intention to become citizens of the United States, who are between
the ages of eighteen and forty-five, and who are residents of the
State, and of such other persons as may upon their own application be
enlisted or commissioned therein pursuant to the provisions of this
division, subject, however, to such exemptions as now exist or may be
hereafter created by the laws of the United States or of this State.
* * * * * * * * * * * *
128. The unorganized militia may be called for active duty in case
of war, rebellion, insurrection, invasion, tumult, riot, breach of
the peace, public calamity or catastrophe, or other emergency, or
imminent danger thereof, or may be called forth for service under the
Constitution and laws of the United States. Whenever it is
necessary to call out any portion of the unorganized militia, the
Governor may call for and accept as many volunteers as are required
for such service, under regulations provided by this division.
Source
California Military and Veterans Code