The spring Equinox was marked by something unique in far Southeastern Colorado on a foggy March morning.

Markings inside a cave lit up at sunrise for a short time. It is believed the markings were carved into the rock face more than 1,000 years ago. They were discovered in 1976.

There are three panels and they only light up for eight to 12 minutes two days a year -- the spring and fall equinoxes.

The cave is in Picture Canyon on the Colorado/Oklahoma border in the Comanche National Grasslands. There is a natural separation in the sandstone that formed a cave known as Crack Cave.

Although it's a mystery exactly how these markings were placed here, it is certain that these inscriptions, in conjunction with the rays of the sun striking them, precisely mark the equinox.

The cave is locked to prevent vandalism. It is only opened on the equinox in the spring and fall. For more information on when the cave will be open, contact the Springfield office of the Commache National Grassland at 719-523-6591. For more information on Crack Cave, Picture Canyon, and the area, click here.

Learn more about the cave markings, dinosaur tracks in Colorado, climbing your first 14'er and much more on Mike Nelson's Colorado airing Tuesday, August 14th at 9:30pm on 7NEWS. Mike will talk with photographer John Fielder about John's favorite spots in Rocky Mountain National Park and how a sight in the park made John move to Colorado. And 7NEWS forecaster Lisa Hidalgo takes us to a backcountry cookhouse for the views and a gourmet meal. We hope you'll joins us for Mike Nelson's Colorado!