SANTA FE, N.M. (AP) - Members of the public haven't been allowed to walk across the historic and massive Elephant Butte Dam 200 miles south of Santa Fe for more than a decade.

Now, on Jan. 7 for one day only, the public can again tour the 25-story, nearly century-old dam that backs up the Rio Grande to form New Mexico's largest water body. The dam also has played a key role in the water politics and disputes among Colorado, New Mexico, Texas and Mexico.

The Santa Fe New Mexican reports that the tour is being offered next month as part of Sierra County's events surrounding its centennial celebrations. The dam has been closed to visitors since Sept. 11, 2001.

The American Society of Civil Engineers has designated the dam a National Historical Engineering Landmark.

The dam was built in the early 1900s by the then-fledgling U.S. Bureau of Reclamation to control flooding, supply irrigation to hundreds of farmers and to resolve problems over the shared Rio Grande.

As farmers and families settled in Colorado and New Mexico, they began using an increasing amount of water. Texas and Mexico complained they weren't getting their fair share. The reservoir was the answer.

Like many dams built during a time when hand tools and mules were used, Elephant Butte was an engineering marvel.

Originally called Engle Dam, it stood 301 feet high and was 1,674 feet long when it was finished. It took 618,785 cubic yards of concrete - more than 20 times the amount used for The Pit at The University of New Mexico - to make a dam massive enough to hold back more than 2 million acre-feet of Rio Grande water.

Today, the reservoir created by the dam also is a primary recreation spot for sailors, boaters and anglers.