Question: Laton Alton Huffman was an American photographer who worked at an Army post  situated on the south bank of the Yellowstone River, at the mouth of what?
Sentence (from "Uncle Tom's Trail"): The trail was constructed in 1898 by park concessionaire, "Uncle Tom" H. F. Richardson when the Department of the Interior granted Richardson a permit to operate a ferry across the Yellowstone River.
Relevant evidence: No