収束ゾーンでのライフ: Life in the Convergence Zone

Aha! Thank you; that's enough information for me to find it, and I should have thought of looking there before: It's Title 10(A)(I)(13)(311) (http://www.law.cornell.edu/uscode/html/uscode10/usc_sec_10_00000311----000-.html).

The "organized militia" are the National Guard. The "unorganized militia" are all of the other able-bodied males ages 17-44 years old inclusive. (Because of the way the definition is written, females can't possibly be part of the "unorganized militia," only the organized one.)

So you're right in a technical sense, but the practical sense was what I was getting at -- in practice, only the "organized militia" is ever called out under Presidential authority, and the "organized militia" is the National Guard.