Sliding Hill Gains Speed; Crews Work to Contain It : Geology: Earth threatening Rowland Heights homes moves six feet in seven hours. Response is two-pronged: creating dike of compacted soil and removing the crawling dirt.

It’s a nightmare on Morning Sun Avenue, says resident Sharon Bowler of this otherwise peaceful Rowland Heights neighborhood.

The earth is on the move again, after slowing to a comfortable creep last week. The previous week, the hillside was cruising along at four feet a day, prompting county supervisors to declare a state of emergency. But in a 24-hour period during the weekend, it slid eight feet more--six feet in seven hours on Sunday.

“Last night, everything broke loose,” Bowler said Monday. “It was moving at three feet an hour. You can actually see it. It’s phenomenal.”

Dozens of huge earth-moving machines from the county and the local school district are trying to move mountains (or at least hillsides) to stop the slide from slamming into the houses on this cul-de-sac. But residents and some geologists have their doubts.

“Sometimes, it can be like sending a 170-pound back to stop a 300-pound linebacker,” said Tom Henyey, a geologist at USC.

Geologists at the site have dug out an enormous trench, hoping to divert the flow of dirt and mud. But it’s not at all clear whether mere mortals can stop the massive slide. It all depends on the kind of mountain they’re trying to move.

The hill near Morning Sun Avenue sits on a thin layer of slippery clay, about a millimeter thick, according to Ed Harp of the U.S. Geological Survey, who visited the site Friday.

Clay is slick to begin with, but recent rains have turned it into a lubricant, like oil. The layer of dirt on top is up to 30 feet thick. Once it starts to move down its slippery slope, it’s not easy to stop.

But geologists don’t consider this a very big slide--on geological scales at least--and the earth-moving equipment is enjoying some success.

The first tactic was to carve out a trench and fill it with more stable earth--creating what is essentially a dike of compacted earth to hold back the ooze sliding down the hill.

The second tactic is to get rid of the hill. In the past few days, “they’ve removed virtually the entire hillside behind those houses,” said Diamond Bar City Councilman Clair Harmony.

Onlookers said that in the past week, the once-serene, grassy hillside has been completely transformed. Now, said one neighbor, “It looks like they’re building a shopping mall. It’s something out of Tonka Toy hell.”

The brute force approach was ordered by the Walnut Valley Unified School District, which owns some of the land and is taking a good share of the blame for the recent slide. In preparation for construction of a new middle school, the district starting moving 1 million tons of dirt in November.

“I’ve been here for 20 years,” said Bowler, a local real estate broker, “and we’ve never had a problem on the hill. We were just amazed. The homeowners think what caused the pressure was that mound moved by the school district.”

Some geologists are blaming the rains, and others are saying these kinds of shifts are simply par for the course in California: Anyone who lives around here knows that terra firma isn’t as solid as it looks. For Southlanders, the earth moves.

School district officials have hired their own geologists to look into the problem. Meanwhile, they’re attempting to remove the threat to the handful of houses on Morning Sun Avenue.

“They’re just trying to keep up with it,” said geologist Harp. “They’re trying to dig most of the material away. The problem is: They don’t have any place to put it.”

In some cases, however, trying to remove the mountain can backfire, commented Henyey, adding, “It’s a two-edged sword.” The weight of the earth contributes to the pressure pushing downhill, but the same weight adds to the frictional forces that keep it from sliding.

“You have to try it for a bit to see what happens,” Harp said. “You may win or may not.”

He thinks the construction crews at the site can probably succeed on this one.

“Unless something strange happens, I think they’ll be able to do it,” he said.

The bottom line, he said, is that you can move Mother Nature. But it has a price.

At this point, neither county nor school district officials are willing to estimate the cost of this project. But Harp said: “It won’t be cheap.”