Beginning more than 200 years ago, the Cowan family has kept letters written to one another, as well as correspondence with eminent outsiders like Ralph Waldo Emerson, sermons given by preachers in the family and multipart essays sent home while traveling. The collection, at least 75,000 documents totaling hundreds of thousands of pages filling 200 boxes, is one of the largest private family troves that has turned up in recent years.

It has been stored in attics, sheds and storage lockers over the years, and most recently in the Cowans' home here in Boulder, where they were interviewed on a recent morning. Its contents cover the scandalous (a relative jailed for embezzlement), the intriguing (a runaway slave seeking refuge in the North) and the historic (the settling of Chicago).

Now the current owner of the collection, Mr. Cowan's grandmother, Mary Leslie Wolff, who is 82, is negotiating to donate the papers — called the Ames Family Historical Collection, for her father's branch of the tree — to a historical society somewhere back East, where the family began. Ms. Wolff declined to say where the collection might go because discussions were continuing.