Before there were "Welcome to Colorful Colorado" signs at the state line, state borders were marked with concrete obelisks. I'd love to know how many still exist on long-abandoned highways on the fringes of the state. You'll find very few along modern border crossings, as you'll see if you visit my project, "Welcome to Colorful Colorado: 40 Views from the Border."
One of the most prominent state line obelisks is west of Grand Junction on the Utah line. Old U.S. Highway 6 & 50 splits away from Interstate 70 at Mack and runs roughly parallel, but a mile or two to the north of the freeway as a mostly unpaved county road. Before the interstate was constructed, this was the main highway route between Grand Junction and Salt Lake City.
Seen mainly by the few residents living nearby, ranchers and oil and gas well servicing trucks, the state line marker obelisk along Old US 6 & 50 marks Utah on one side and Colorado on the other. The marker has been defaced by bullets, graffiti and the ravages of time. It's anybody's guess how long the marker will remain there.
Here's more of what you might find along Old 6 & 50 west of Mack, Colorado: