American scholars haven't done too bad a job in documenting the early folk song scene - far better than has happened in the UK as far as I can make out.
For early overviews see Josh Dunson's 'Freedom in the Air' - song movements of the '60s; Oscar Brand's 'The Ballad Mongers' - rise of modern folk song; John Greenaway's 'American Folksongs of Protest'.
Lomax's 'Penguin Book of American Folk Songs' (companion to English, Scottish, Australian, Canadian, Ballads... et al) are invaluable anthologies, and themed collections like Archie Green's 'Only a Miner' are goldmines of information a well as rich sources of song.
Would highly recommend some of the Lomax biographies that have recently emerged - and his autobiographical 'Land Where the Blues Began' - magic.
If you can lay hands of John Lomax's 'Adventures of a Ballad Hunter'.....
None of these are without problems, but It's difficult to know where to stop really.   
Good Luck
Jim Carroll