The Oregon-California Collection is an artificial, or subject-based, collection comprising of a variety of documents that have been placed in this collection over the years due to their common subject matter. The collection consists primarily of letters, diaries, and articles from Missouri newspapers relating to overland travel to Oregon and California in the 1840s and 1850s. Most of these items are transcriptions or reproductions, rather than original documents. The collection also includes correspondence of the Missouri Historical Society with various individuals, 1924-1940, mostly relating to papers and publications about 19th-century overland travel to California and Oregon.