An localized internet blackout (IMO) could only be accomplished if the .gov is working in conjunction with local ISPs. For "last mile" providers like Comcast and AT&T...this COULD be relatively easy as you don't need "boots on the ground" from the providers to turn off service connections. A more detailed discussion of this quickly becomes "local" in the sense that retail customers of ISPs in that area are probably set up using various configurations of very small aperture terminals (VSATs) may also use satellite links to transport traffic to middle mile facilities or directly to the national backbone networks.
How they would go about blocking satellite access...is beyond my scope of knowledge. But my point is, a localized disruption is NOT entirely impossible.
An addendum to my post above...as I thought of it...ISPs (under coercion from .gov) could also blacklist a certain number of sites (Twitter/Facebook/Livestream/GMail/etc.) locally pretty easily, without totally blacking out the entire connection to the web. Turning OFF upload bandwidth locally (i.e. making the ISPs internet connections read only or download only) is also possible.