Chicago Style
The Chicago Manual of Style refers to archival collections as "Manuscript Collections." For more detailed guidance, check out sections 14.232-14.242.
Chicago Notes Example: Photograph, "Lisa Ben" [ca. 1965], Box 4, Folder 1, Lesbian Legacy Collection Subject Files, ONE Archives at USC Libraries, USC, Los Angeles, CA.
If you've cited one item from an archival collection, the name of the item or its creator is usually the main element in the bibliography entry. If you've cited more than one item from an archival collection, the name of the collection is usually the main element in the bibliography entry.
Chicago Bibliography Example if using multiple items from the collection: Ben, Lisa, Lesbian Legacy Collection Subject Files. ONE Archives at USC Libraries, University of Southern, CA. Los Angeles, CA.
APA Style
These are called archival documents (e.g., a diary, limited-circulation brochure or pamphlet, unpublished manuscript); see Section 10.8 of the Publication Manual of the Psychological Association, 7th edition for additional information and examples.
APA General Format: Author, A.A. (Year, Month Day). Title. [Description of Material]. Name of Collection (Call number, box number, file number, etc.). Name of Repository, location.
APA Example: Brittain, V. (1950, June 1). [Letter to XYZ]. Lesbian Legacy Collection Subject Files (Box 4, Folder 1. Coll2009-004). ONE Archives at the USC Libraries, Los Angeles, CA.