As another archaeologist on this list, I can say that specializing in a particular locality would make one a very (much more than usual) monetarily poor archaeologist. Many archaeology (CRM) firms operate within a radius of their home office. There is a lot of travel involved, even for "local" work.
On another note (and to address the original matter), there is the possibility of doing limited site research at a site like MaryAnn Forge, but it would require a knowledgeable individual, permission from the State Park Superintendent, and also a nod from the State Historic Preservation Office. I know this because it is what I needed to examine the Brooksbrae site in BBSF. Sometimes if the circumstances are just right, and in the hopes of examining a site before losing it to vandals and looters, you can get permission to perform a very concentrated study of the site. My research at Brooksbrae, for instance, consisted mainly of mapping, documentation of the structural remains, and very limited shovel-tests (only with the permission of the Park Superintendent himself - in fact, he helped screen the tests).
So, if you know an archaeologist and can jump through all the hoops to get your research authorized, then yes you can do a limited investigation. However, for many non-archaeo types, it is always well advised to keep the State Park informed of looters and "treasure hunters". For BBSF, you would want to keep Chris Bethmann in the know, he has a passion for the forgotten town sites, and usually will increase patrols if there are reports of suspicious activities.
Hope this helps.
Scott W.
