Road following a fence line leading to the Utah Arizona Nevada tri-state marker. A sign at the intersection points the way to the marker.  

The 15mph speed limit signs are for the UNEV pipeline construction access roads.

"UNEV is a 400-mile, 12-inch buried, common carrier products pipeline that will originate near the refineries in North Salt Lake City and ship product from them to a distribution terminal in Iron County, Utah, and a terminal in North Las Vegas. The Pipeline will initially have the capacity to carry approximately 62,000 barrels per day of petroleum products but will have the capacity to run 118,000 barrels per day through it."  see http://www.unevpipeline.com/