The area had been made up of a mountainous and rocky surface, with a low population due to the unstable soil in the region.

The visitor center was closed in 2006 due to structural damage from unstable soils.

McCrae's gravestone is placed flat, as are all the others in the section, because of the unstable sandy soil.

He also was concerned, he said, that unstable soil would eventually cause the building he had designed to settle.

Very few buildings had been built to withstand an earthquake, and the city lies on unstable alluvial soil.

A cliff, maybe thirty feet high, was cut into the hillside where the undergrowth had let go of unstable soil during the previous winter's snows.

In addition, unstable soil led to the collapse of several sections of tunnel being constructed.

When combined with the maintenance issues associated with the unstable soils, these factors lead to very high infrastructure costs for urban development within the valley.

House Bill 3375 required that new construction on slopes of 20 percent or greater with unstable soil undergo increased regulation and an extended approval process.

This was required due to the unstable, water-logged soils and the need to avoid settlement damage to close-by buildings.