Time and Place
What is the fictional date of Canyon Passage (1946)?
The open includes a title saying: "Portland Oregon 1856". Furthermore, the first day is a rainy Saturday since the next day is said to be Sunday. So that leaves approximately 52 possible days in 1856 for the story to start in - a calendar for 1856 would be necessary to determine the exact number and the dates of those Saturdays.
The protagonist predicts that he will reach Jacksonville by Friday on horseback, thus indicating that Jacksonville is in Oregon and not Washington, because crossing the mighty Columbia River wasn't mentioned.
There doesn't seem to be a Jacksonville, Washington, but the town of Jacksonville, Oregon is about 250 miles south of Portland as the crow flies, and 271.7 miles by the straightest modern road I-5 S, and 338.0 miles by US-26 E and US-97 S. So five to six days of riding would be 45.28 to 67.6 miles per day, and 4.528 to 6.76 miles per hour assuming 10 hours riding per day.
Characters discuss making a trip of a few weeks to San Francisco and back, which would be optimistic if riding the whole way. I suspect that they planned to ride to a port and take a coastal ship. Crescent City, California (also known as tsunami central) looks about 70 to 80 miles from Jacksonville, Oregon as the crow flies, and is 108.9 miles by US-199 S as it circles around the mountains.
Jacksonville, Oregon is also about three miles from the Rogue River, which is significant to those who know Oregon history. The Rogue River Wars is the name of a conflict with various tribes called the Rogue River Indians by whites that lasted from October 8, 1855 to June 1856.
Jacksonville, Oregon was founded as a gold mining camp about 1852, so paying with sacks of gold dust seems fairly reasonable.
I suppose that Ernest Haycox, writer of the 1945 novel Canyon Passage in the Saturday Evening Post, was responsible for most of what is historically accurate in Canyon Passage (1946), and the creators of the movie are responsible for most of what is inaccurate, such as the starting date and the events of the war.