There was a woman in the 50's, who wrote a book called Saddle Tramp, about just such a trip. She was the only one left of her family, and was in her 60's, and had one horse, and bought another for a pack horse, and set out from Maine to California.
She appeared on the Art Linkletter show, he had heard about her, and about one of her horses dying due to bad feed I think, and bought her another one to continue her travels with.
She made it, and that was before cell phones.
And in 80's there was a woman I was friends with who came from CA to D.C. with a small mule and a covered wagon all by herself. Someone gave her a German Shepherd dog, and she was doing it for the vets.