American literature will usually be assigned a call number in the "PN" or "PS" range; here's a quick outline of call numbers and their classifications:
PN1-6790 - Literature (General)
PS1-3576 - American Literature
PS126-138 - Biographies
PS147-152 - Women authors
PS185-195 - 17th-18th centuries
PS201-217 - 19th century
PS301-326 - Poetry
PS330-353 - Drama
PS360-380 - Prose
PS430-439 - Humor and satire
PS451-478 - Folk literature
PS700-3576 - Individual
These books are in the reference collection and prove to be good places to find authors, background information and topics which may help you start your research.
Greenwood Encyclopedia of Multiethnic American Literature by 
Encyclopedia of African American Women Writers by 
Greenwood Encyclopedia of American Poets and Poetry by 
The Greenwood Encyclopedia of World Folklore and Folklife by 
The Greenwood Encyclopedia of African American Literature by 
