The date is October 16, 1882 and Hollister compliments Elizabeth Blythe on her fine stories about the building of the Panama Canal. Construction on the Panama Canal started in 1904, a full twenty-two (22) years later. Although the idea of a canal dates back to the Spanish in 1513, the United States did not consider building it until the late 1890s, still a decade later than the date of the story.
The gang plans to kidnap the two riders, except that the gang cannot possibly know that either rider was headed to the fort nor what trail since Blythe Danner told no one of her plans. This is a common error made by writers where they assume characters have more information than they could possibly have.