In northwestern New Mexico lie the monumental remains of a vanished culture. Over a thousand years ago in Chaco Canyon, the Native American Anasazi established a series of settlements that included elaborately irrigated fields, a vast system of roads, and hundreds of stonemasonry structures, built from carefully cut blocks of sandstone. The most erosive factor is water. In winter, snow piles up on the tops and at the base of the walls. When it melts, the water percolates down from the top, freezing at night within the walls and causing the masonry to buckle.
Snow melting on the ground leads to rising dampness that erodes the base of the walls.
Torrential thunderstorms during summer months cause surface erosion of soil and loss of mortar in the masonry. And, as at so many archaeological sites around the world, the demands of increasing visitation and of continuous protection of the ruins far exceed existing resources. In 1991, the NPS and the GCI began a project to test strategies for protecting architectural remains such as those at Chaco. The project was based on the use of backfilling as a protective measure that is flexible and easily reversible, one that reduces maintenance while permitting visitation and interpretation of the site. Although backfilling has long been practiced as a means of preserving archaeological remains, its effectiveness has never been systematically studied.