The collection consists of the papers of Samuel A. and Harriet T. Clarke, including diaries and correspondence. One of the diaries is Harriet T. Clarke's 1851 diary that covers her overland journey from Iowa to Oregon, and includes descriptions of landscapes, weather conditions, and campsite locations. There are three versions of this diary: the original, which only describes her journey up to when she was near Salt Lake City; a typescript copy of the original; and a partial handwritten copy from a later date, which includes entries relating to the later part of her journey, including her arrival in Oregon. The other diaries are Samuel A. Clarke's original diary from 1845, and a photocopy and typescript copy of his diary from 1850 to 1853 and 1879. Correspondence in the collection includes letters from Joaquin Miller, Jesse Applegate and his daughter Sallie Applegate, and James W. Nesmith, as well as George Curry, Joseph Lane, and Edward Baker.

Other materials in the collection consist of essays and poems by Samuel A. Clarke; Clarke's reminiscences about traveling to the Shasta mines in 1851; a scrapbook compiled by Clarke about the issue of free silver during the 1890s; writings and reminiscences relating to Oregon history; an affidavit regarding Clarke and an attached certificate; biographical and genealogical materials; and souvenir programs, one of which postdates both Samuel A. Clarke and Harriet T. Clarke, and may have belonged to one of their children.