Correction of adverse conditions through engineered design and construction may be an acceptable mitigation technique if the methods are supported by careful investigation and evaluation, by a registered geotechnical engineer or by an engineering geologist registered in the state, of the physical extent, seriousness and causes of geologic problems. Those methods may involve, among others, refraining from removing natural support materials in the area, addition of artificial support to the area in the form of rock or earth fill buttressing, retaining walls or cribbing, concrete slurry, rock bolting and reinforced pilings, permanent improvement and control of surface and subsurface drainage, and stabilization of the slide area by bridging weak zones, removal of unstable material, and avoidance of loading on unstable areas.