MLA

Stein, Gertrude, 1874-1946. "Preciosilla". Box 153, folder 3794. n.d.. https://collections.library.yale.edu/catalog/9998189.

APA, 6th edition

Stein, Gertrude, 1874-1946. (["Box 153, folder 3794"])(n.d.)["Preciosilla"]. https://collections.library.yale.edu/catalog/9998189.