Captain Carlos Alvarez De La Mesa Collection - 39th New York Infantry Regiment
This collection was donated by Allison Lassoe of Sheffield, MA. It includes, among other items, over 100 letters written by Carlos De La Mesa to his wife, Fannie (most in Spanish); War Department documents; pension applications; an image of De La Mesa; even a lock of his hair.
This collection was partially arranged, transcribed and translated by Amanda Rodriguez, a student from Skidmore College.
As part of her internship Ms. Rodriguez wrote an introductory essay.
You can find translations of the letters here.
A newspaper article on the collection is here.