LAS VEGAS — Another southern Nevada relic is emerging as drought lowers the water level at Lake Mead.
Months after foundations of buildings in the old LDS Church town of St. Thomas became visible near Overton, the subsiding water has revealed a concrete water tank from the construction of Hoover Dam in Boulder Basin.
The circular structure, 15 feet deep and 115 feet across, was built in 1931 to clean Colorado River water used to wash gravel. Seven years later, it disappeared beneath the rising waters when Lake Mead was filled.
Kay Rohde, interpretation chief for Lake Mead National Recreation Area, called the tank a piece of southern Nevada history.
The structure was built into the side of the Boulder Hills to provide a settling basin for sediment-rich Colorado River water. Clarified water was then piped to a screening plant about 130 feet below, to wash gravel used to make concrete for the dam.
When the dam was finished and lake was filled, the Boulder Hills became the Boulder Islands and the tank disappeared below the surface of the lake.
Drought has reversed that process. Since 1998, when the lake was near capacity, the water level has dropped 80 feet, leaving a white mineral ring, prompting modifications at marinas and reducing the amount of lake shoreline from 700 miles to about 500 miles.
The Hoover Dam reservoir is at its lowest level since 1968, at 1,129 feet above sea level on Monday. The lake is still more than half full, with about 4.5 trillion gallons of water. Las Vegas water intakes are at 1,050 feet and 1,000 feet above sea level.
Officials say the next man-made structure to surface could be the foundation of a 10-by-20-foot pump house near the clarifying tank.
"Every day it's the lowest I've seen it," said Jim Koza, a National Park Service navigation specialist who has worked at Lake Mead for 30 years. "Almost all of Lake Mead is changing so rapidly that what you saw out there four weeks ago is completely different than what you'll see next weekend."