The research files on Swiss, French, Belgian and German pioneers of Dallas were used in the writing of Mary Ellen Holt's Swiss Eyes on Dallas: Late 19th and Early 20th Century Pictures by Emil Fretz (Word Merchant Press, 2016). Though the research files primarily regard Swiss families, they also document French, Belgian, and German families, a number of whom were settlers in the La Reunion colony located in what is now parts of the Dallas neighborhoods of Oak Cliff and West Dallas. The files were used by Holt to identify and augment information on Fretz' photographs. The newspaper clippings are photocopies of downloaded articles dating from 1856 to about 1926.

Included is a series of photographs made by Emil Fretz, an amateur photographer. Subjects include of his family, friends, and activities in Texas. Collection consists of albumen prints and snapshots made mostly between 1898 and 1928, though many are undated.

Of particular note are images of the community of the freedmen's community Little Egypt, White Rock Creek prior to development of White Rock Lake, early Dallas parks, and residences in the neighborhood surrounding Liberty Street, formerly known as Germania Street.

Emil Fretz (1858 - 1928) was a Swiss immigrant and barber who came to Dallas in 1870, was appointed to the first Dallas park board in 1905. His appointment began a 22-year career in public service that extended into his retirement years. One of the major accomplishments during his tenure was the establishment of Trinity Play Park in the disadvantaged area known as the Cotton Mills. Upon his retirement from the board in 1927, Trinity Play Park was renamed Fretz Park in his honor; a second Fretz "North" Park opened in 1964, and after the first one was closed it became the sole Fretz.

Mary Ellen Holt is an antiques dealer and local historian in Dallas, Texas.