Jacob Oliver Hays was born in Missouri in 1831. A gunsmith by trade, he arrived in the Colorado Territory in 1871 where he began doing odd jobs in many locations: Denver, Jim Creek, Ward, St. Vrain, Left Hand, Valmont, Big Thompson, Burlington, Longs Peak, Gold Hill, Boulder City, Four Mile Creek, Penn Gulch, Sugar Loaf, and Bummer Gulch. Most of his time in the late 1870's was spent in the Four Mile Canyon area.
Hays refers to many people, often using simply initials instead of their full names. He describes the weather, prospecting, fishing trips, collecting berries, hunting, digging a ditch from North Boulder to Four Mile, sawing shingles, tearing down Hunt's Mill, hauling railroad ties, and other odd jobs.
On October 7, 1873 he "commenced work with J. Mincer at saw mill [Horton Mill] mouth of Four Mile junction with Boulder Creek at forty dollars per month." On January 18, 1874 he was hired by Mr. Hunt "to tear down old mill building." On March 5, 1874, "Hunt buy Horton out, mill, mining claim, & all."