[3] He became prominent in politics and business in Fort Collins after the founding of the town in 1867, and served in several official posts, including becoming Sheriff of Larimer County in 1871.
[1] After spending a year in Mississippi, in early 1859, Mason travelled to St. Louis, Missouri and joined the Raynolds Expedition which was traveling west to explore the headwaters of the Yellowstone River, but Mason left the expedition, before it was complete, in the winter of 1859-1860 while they were wintering over in Deer Creek Station in central Wyoming.
[2] From there, Mason traveled south to Laporte, Colorado, arriving on February 10, 1860, where he found a settlement of mountaineers, trappers, and Native Americans.
[2] Mason briefly left Laporte to spend time in the mining camps, but returned to the area to settle 4 miles downstream from the town in 1862.
[3] Upon returning to the Cache la Poudre valley, Mason purchased a 160 acre[4] tract of land from a Native American woman who was the recent widow of a man named Gangros.
[3] He suggested that this ground would be high enough to be safe from flooding and would allow a good vantage point for spotting impending attacks from hostile Native American groups in the area.
[6][3] Once the county seat was moved to Fort Collins, the courthouse was located on the second floor of the Old Grout sutler's store building.
[2] During his time as sheriff, Mason arrested noted criminal Happy Jack, but he subsequently escaped custody.