The Trail archive is our collection of full-text period documents. There is a lot here; you could spend a career studying it.
Diaries are first-hand accounts of the Trail experience written during the journey. Not to be confused with memoirs (See below) diaries are the best historical evidence we have of the true Trail experience.
Memoirs are first-hand accounts of the Oregon Trail journey written many years after the fact. They are not as historically reliable as diaries, but they still tell a fascinating tale.
The full-text of books written during the overland period. Most books written along the Trail were guides designed to help future travelers.

