From the Smithsonian article "Horse-Riding Librarians Were the Great Depression’s Bookmobiles" by Eliza McGraw:
During the Great Depression, a New Deal program brought books to Kentuckians living in remote areas.
In 1936, packhorse librarians served 50,000 families, and, by 1937, 155 public schools. Children loved the program; many mountain schools didn't have libraries, and since they were so far from public libraries, most students had never checked out a book. "'Bring me a book to read,' is the cry of every child as he runs to meet the librarian with whom he has become acquainted," wrote one Pack Horse Library supervisor. "Not a certain book, but any kind of book. The child has read none of them."
Read the full article and see more photos here.