Monday, May 16, 2005


Submerged gravel plant toured


Review Journal
By Henry Brean
May 14, 2005

Park Service diver Dave Conlin, left, steers a foot-long,
remote-operated submarine Friday, as Boulder City Museum
curator Dennis McBride, middle, and former Hoover Dam
construction worker Lee Tilman watch images of a submerged
gravel plant 150 feet below. Tilman, now 92, made several trips
to the plant in his job as a truck driver more than 70 years ago.
Photo by Gary Thompson.

Condition of lake's underwater historic sites being assessed
From 1931 to 1935, a gravel plant in the Boulder Hills churned out about 1,000 tons of material an hour for the concrete in Hoover Dam, sealing its own watery fate pebble by pebble and rock by rock.

What remains of the plant now sits under about 150 feet of water in Lake Mead, submerged there by the dam it helped build.

On Friday, a foot-long, remote-controlled submarine beamed back ghostly images of rock piles, train tracks and discarded machine parts, as a team of divers from the National Park Service prepared to explore the site in person.

The team from the Park Service's Submerged Resources Center in Sante Fe, N.M., is scheduled to dive to the plant today and Sunday from a houseboat anchored above it.

The operation, which is being funded with money raised through the sale of federal land in the Las Vegas Valley, is part of a larger effort to determine the location and condition of underwater historic sites throughout Lake Mead.

As the lake's water level drops, the survey should help Park Service personnel better predict "when these sites will come out (of the water) and how to protect them," said Dan Lenihan, who helped start the Park Service's archaeological dive team in the 1970s.

Lenihan still works with the unit part time, despite his retirement in 2000.

Lenihan's job has taken him on dives from the Pacific islands of Micronesia to a limestone sink known as Montezuma Well in the middle of the Arizona desert. In between, he has made "a couple hundred" dives at Pearl Harbor to inspect the condition of the sunken battleship USS Arizona.

The underwater assessment at Lake Mead has just begun, Lenihan said, "but we're really determined right now to find out what's down there. We've been talking to the local diving community to see what they know."

It's hard to steer, but this foot-long,
remote-operated submarine is perfect
for scouting submerged historic sites,
says National Park Service diver Dave Conlin.
Photo by Gary Thompson.

And that led, in part, to this weekend's dive mission.

"It's a pretty popular dive site for technical divers," said Dave Conlin, who heads up the Submerged Resources Center dive team.

In its day, the gravel plant was used to sort aggregate by size from sand to 9-inch cobbles. During its roughly four-year life span, it produced enough rock material to make 4.5 million cubic yards of concrete, roughly the amount used to build the dam, power plant and related facilities.

Among those brought in to observe Friday's pre-dive scouting trip was 92-year-old Lee Tilman, who watched the live video feed from inside the houseboat.

"I thought those gravel piles would be covered in sediment by now. I guess they aren't," said Tilman, who has lived in Boulder City for as long as there has been a Boulder City. "This is a fantastic experience to come back and see this."

Tilman worked as a truck driver during the construction of Hoover Dam, a job that involved several trips to the gravel plant. What he remembers most are the crane operators, who swung a clam-shell scoop filled with rock from the end of a 200-foot boom and never seemed to miss their targets.

"That impressed me more than maybe anything else about the operation," he said.

Later, as a member of the Civilian Conservation Corps, Tilman helped remove buildings from the soon-to-be-flooded St. Thomas town site and took part in an effort to collect American Indian relics before the lake was filled.

He said some of the pottery he rescued is still on display at the Lost City Museum in Overton.

The places Tilman and others once looked for artifacts could be targeted for future dive operations. Conlin's team is expected to return to Lake Mead this winter to search for more submerged artifacts.

But Conlin had little time to think about that Friday. He was too busy trying to steer the little submarine, which looked more like a child's toy than a sophisticated scientific instrument.

"It's hard," he said, fighting the controls. "I think if we were 7 years old and grew up playing video games, it would probably be easy."

The submarine's camera films a silt-covered
stretch of railroad track at the site of a 1930s
gravel plant now at the bottom of Lake Mead.
Photo by Gary Thompson.

As the submarine moved through water, particles of silt seemed to rush toward the camera lens like snowflakes. After circling the site, Conlin parked the sub over a short stretch of railroad bed that still had its tracks.

According to Dennis McBride, curator of the Boulder City Museum and Historical Association, there would have been an almost steady stream of trains hauling rock between the gravel plant and the concrete batch plants at the height of dam construction.

So how does an old gravel operation that was stripped of most of its equipment and unceremoniously left to be swallowed by a lake now rank as a place worthy of preservation? The same way a lot of historic sites do, Lenihan said.
"Archaeology is really the study of the mundane. Things that seemed to have no significance then have a lot of significance now," he said. "It's the seemingly unimportant stuff, that's where the story is."


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