What are those pillars at the City of Boulder border?

On the Northwest corner of Arapahoe Road and US 287, stand two large sandstone pillars. For years I have wondered why these pillars were built. They sit right on the west border of Boulder, Colorado. You can tell they are old and not maintained. I searched for years on the internet for some explanation. But I just didn’t know the right keywords until now. Because they have made the news in the recently. Come along with us as we take you to the pillars and tell their story.