Show specific categories of posts on sub sites

I’m looking for a plugin or any way really to do this:

I have a large multi-site set up. The main site will have tons of posts on it, however I want to be able to categorize them by area/location (i.e. Colorado)

Say there are 3 sub-sites that are ‘zoned’ Colorado, (i.e. Denver, Longmont, and Boulder sub-sites.) I’d like to be able then go into each sub-site and say “Show posts from Colorado.”

They’re all on the same server, however each will have a different URL.

I seem to be able to find things that will allow sub-sites to transfer posts up to the main site, but not the reverse. Any ideas?

Thanks!