The Union Hill Mines, which began in 1862, were located up the western slope of Union Hill from the mouth of Weaver Creek at the head of Union Gulch and became one of the largest placer mines in Trinity County. Water was first ditched from Weaver Creek and Little Brown’s Creek. In 1904, Peter M. Paulsen acquired control of enough claims to construct a 15 mile ditch from Grass Valley Creek that collected water from Sawmill and Tom Lang Gulches. He built a 165-foot bridge on two concrete piers to support a 5,000-foot siphon through a 30-inch pipe, with the outlet dropping 300 feet in elevation into a 6.5-by-4.5-foot tunnel 570 feet long that emptied into the mine’s upper holding pond. The overcantilever and flat steel bridge was wide enough for the pipe and a wagon. Paulsen sold the property to Trinity Consolidated Mining Co. in 1911. In 1921, Tacitus R. Arbuckle leased the mine, and continuous operation ceased in 1928. The bridge was dismantled for scrap at the beginning of World War II.