This small collection contains primarily Detwiller's student drawings, notes, course materials, books, class photographs, and graduation announcements from the period of his study at Columbia University from 1881 to 1885. These materials are supplemented by a small group of Detwiller's childhood sketchbooks, drawings and office papers created by Detwiller during his practice as a professional architect, and other scrapbooks and ephemeral items relating to Detwiller's family and personal interests, spanning the years 1874 to 1940.

Collected by Jeanne Kleinfield Welcher (1923-2010), great granddaughter of Samuel Putnam Avery Sr. (1822-1905), this collection contains materials pertaining to the philanthropic efforts of the Avery Family during the late nineteenth and early twentieth centuries in the United States. The collection contains institutional documents, professional and personal correspondence, newspaper clippings, visual and research material, and personal affects pertaining to three generations of the Avery Family.