Maya Angelou’s paper trail includes a rambling, typewritten letter from James Baldwin, dated Nov. 20, 1970, addressed to “Dear, dear Sister” discussing everything from his new book to his feelings about death.

And one from Malcolm X, written on Jan. 15, 1965, assuring her, “You can communicate because you have plenty of (soul) and you always keep your feet firmly rooted on the ground.”...

All of these things and more — a total of 343 boxes containing her personal papers and documents — have been acquired by the Schomburg Center for Research in Black Culture. The trove has notes for Ms. Angelou’s autobiography, “I Know Why the Caged Bird Sings”; a 1982 telegram from Coretta Scott King asking her to join a celebration at the King Center; fan mail; and personal and professional correspondence with Gordon Parks, Chester Himes, Abbey Lincoln and her longtime editor, Robert Loomis....