The 2006 landslide covered the only access road to the powerhouse, and was threatening to send thousands of tons of mud and rock into a narrow section of the South Fork of the American River.

The site posed many challenges. For one, the hill was raked at 55 degrees, almost as steep as the pitch of a teepee. Compounding this was the fact that there were large, open cracks in the slide all the way up the hill, telltale signs that the waterlogged soil was still moving and could give way at any moment.

The geological layer under the mud was found to be also highly unstable. The Carlton team determined that the best fix was to scrape the hill clean of mud, and then drill deep to set massive steel bolts 20 feet into the solid bedrock. The bolts were to be connected to large V-shaped concrete beams set across the hill to keep everything in place. Finally, wire mesh drapery, which looks like heavy-duty chain-link fence, would be set down to prevent the poker chips, now exposed, from breaking free and rolling down the hill.

Anyone working on the hill had to be roped to a harness, and all the heavy equipment – even the D4 bulldozer that scraped the hill clean – had to be secured with cables bolted into rocks above the slide.

To make sure the hill would pose no further problems, a latticed concrete crib structure filled with gravel was placed at the bottom of the hill to prevent the toe of the hill from encroaching on the access road along the river. Finally, a separate run-off control system was built to divert rainwater away from the hill and send it down the sides.