Archaeologists for years have puzzled over the scale and range of prehistoric activities that created the remarkable flint quarry sites at Alibates, Texas. No doubt some Native Americans, in search of flint, merely picked up exposed chunks or cobbles lying on the ground. Others chiseled boulders directly from the bedrock.

Their quarrying activities left holes ranging from small depressions to broad pits from 5 to 20 feet across and up to 2 feet deep. But what catches the visitor's eye are the quarry waste piles and tool-making debris blanketing the slope hillsides hundreds of yards from the pits. There are thousands of quarried chunks, tested cobbles, flakes and tools in various stages of production. Few sites are as dramatic as the Alibates Flint Quarries.

Today, a 1,337-acre national monument protects this mesa-top that literally is covered with a carpet of these flint chips. Although collecting Alibates Flint is prohibited, you can pick up, examine, and even taste chips, as long you put them back.

Flint is usually dark grey, black, white, or brown in color, but unusual colors are a trademark of Alibates Flint Quarries. The flint here is associated with a type of dolomite, which is an anhydrous carbonate mineral composed of calcium magnesium carbonate, and creates distinctive brightly colored flint. Alibates Flint is found in hues and tones of the evening sky; colors ranging from pale grey and white, to pink, maroon, and vivid red, to orange-gold and an intense purplish blue. Patterns vary as well with bands of alternating color that create stripes and a marbled effect.

The quarries were in use between 1150 and 1450 BCE (Before Common Era) by Plains Village Indians, who were the ancestors of the Caddo, Pawnee, and Wichita nations. They lived in large permanent villages as well as smaller outlying farming and gathering communities in the region.

More than 700 quarries were all dug by hand, but to see them you will need an escort. Ranger-guided tours typically are led once a day at 10 a.m., but occasionally a second tour is offered at 2 p.m. Reservations are required for these explorations, which can last up to two hours. Tours includes a one-mile trek to the top of the mesa and to other protected areas where quarries were once four- to eight-foot deep. They have since been filled with soil by wind and rain.

Tools made from Alibates Flint have been found across the Great Plains and Southwest, and was so prized that prehistoric hunters traveled and traded a thousand miles or more to obtain it. Its uses have been dated from 13,000 years ago to as late as the 1870s. A volunteer flint-knapper is on site most weeks to share stories and shape flint into usable tools and weapons right in front of your eyes. It's a fascinating, and noteworthy place to visit.