That’s an interesting question. I found several instances of individuals traveling on riverboats who were robbed or whose rooms were burglarized, but nothing about someone holding up a steamboat. To pull a heist on a riverboat, a large gang would have had to cover such a big transport; plus, the robbers would have needed a good escape plan.
Marshall Trimble is Arizona’s official historian. His latest book is Wyatt Earp: Showdown at Tombstone. If you have a question, write: Ask the Marshall, P.O. Box 8008, Cave Creek, AZ 85327 or e-mail him at firstname.lastname@example.org