The Nu'uanu project marks the first time the state has taken protective measures near a residential area.

Both projects are being done by the Department of Land and Natural Resources, the first time the agency has tackled such work. The Department of Transportation has undertaken similar work, but it has been limited to protecting drivers along state highways.

The entry of the DLNR into rock-fall mitigation is considered significant because the agency oversees nearly the entire inventory of state land — 1.3 million acres out of 1.5 million.

After the Onishi tragedy, Ed Guieb built an 8-foot concrete wall behind his Rooke Avenue home — just below the quarry site — but he knew that would not be enough to stop a large boulder. He wrote to the state asking for protection for his home from falling boulders, and is happy that the project is moving forward.

"I feel comfortable with it knowing they will put up fencing and will remove the loose boulders," Guieb said. "It's also in the best interest of the state due to the liability if anything should happen."

No one has been hurt by rock falls at either of the project sites, and that is how the state wants to keep it, said Morris Atta, special projects coordinator with the land division of the DLNR.

The DLNR is taking other steps in addition to the protective measures. It has brought in an expert from the U.S. Geological Survey for two weeks of intensive classroom and field work to train people to identify areas that could be in danger from falling rocks.

"The more people we can have trained to recognize what risks there are, how to identify situations so that we can prevent damage or injury, then we are all better off," DLNR Chairman Peter Young said.

Draft environmental assessments were filed for both mitigation projects last week with the state Office of Environmental Quality Control, and public comments are being accepted.

Young said the work is not the beginning of a statewide assessment of all potential rock-fall sites, but a growing effort to deal with the most threatening problems and to better understand the risks.

"There are too many slopes in Hawai'i that have rocks that can fall down them," he said. "We are not inspecting every potential rock. You just can't do it. The scale is too great."

The chance of a rock falling at both project sites is moderate to high.

In Nu'uanu, 30 boulders have been targeted either to be demolished or secured in place at the old quarry. According to the state, blasting methods used to quarry rock decades ago has increased instability and raised the potential for rock falls. The $2 million project will include a 20-foot-long, 10-foot-tall fence between the rock overhangs and homes below.

In Pacific Palisades, the $2.3 million project will include a cable-and-mesh net system that will be placed on a steep slope above Komo Mai Drive. A 220-foot-long, 10-foot-tall fence will be installed below a rock cliff.

Area resident Michael T. Jones was surprised to hear about the danger.

"I didn't even know there was a problem," he said.

The road is the only access to the residential neighborhood and, if it were to be cut off by a rockslide, many people would be stranded, he said.

"Pretty much we'd have to have helicopters or something," Jones said.

About 50 people are attending the rock-fall training, Atta said.

Edwin Harp, a geologist and researcher with the USGS, is leading the classes and visiting several sites on O'ahu to train students how to evaluate rocks for the likelihood of fracturing and falling.

"I try to take them to see as many different types of rock that I can, some good, some bad, so they have a chance to see a spectrum of what you have here and to practice rating each kind," Harp said.

He noted the conditions that contribute to rock falls in Hawai'i.

"Everybody agrees that much of the development here has put people underneath cliffs and in valleys," he said. "In the beginning they probably didn't recognize the hazard. As more and more people build into slopes that are pretty steep, you have more exposure to rock-fall hazards and other kinds of landslides, too."

Young said the state and city might need to establish building-code restrictions so homes are not built in risky areas, and some wilderness areas might have to be closed to the public because of the hazards.

"Maybe through this ongoing education, we can say, 'Is there a better way to look at this?' " he said. "Can we put in mitigation measures that can eliminate or reduce the hazards to people or property? With the scarcity of land in the state and a growing population, we are only going to continue putting ourselves in potential challenges."