premise: For three days we joined the anniversary trail ride commemorating the 1874 march west of the original North West Mounted Police contingent; a great adventure which originally took 275 officers and men from Fort Dufferin south of Winnipeg all through the southern part of Saskatchewan and southern Alberta to Fort Whoop-Up 125 years before.
hypothesis: The trail ride took people from one fort to another commemorating a similar march in 1874.
reason: The adventure took 275 officers and men from Fort Dufferin to Fort Whoop-Up and the text implies someone was joining an anniversary commemorating it.