What did five (5) month travelers do? They recorded their journeys in diaries and letters back home, detailing the trip. Ok, not all of them. But you will be surprised where you may find your ancestor's name. Sometimes the diaries are filled with gruesome details as the writer recalls on paper a companion's demise. Sometimes the accounts are so detailed they read like a novel. Sometimes they just follow a train of thought, or confirm a reader's suspicion.
Another great source is the Negro Trail Blazers of California by Delilah L. Beasley; original 1818; reprinted 1969.