The Anaheim Hills Santiago Landslide has always been classified as "Area #4" ever since the City of Anaheim first thought of developing it for homes and condos. The following is a quote from the Landslide Susceptibility section of the Landslide Hazard Indentification Map No. #34 for the Orange Quadrangle, Orange County, California:
AREA 4 - MOST SUSCEPTIBLE AREA. This area is characterized by steep slopes and includes most landslides (whether apparently active at present or not) and slopes upon which there is substantial evidence of downslope creep of surface materials. Slopes within Area 4 should be considered naturally unstable, subject to failure even in the absence of the activities of man. This area is subdivided into two subareas: (1) SUBAREA 4-1, generally located outside mapped landslide areas, contains unstable slopes underlain by both weak materials and adverse geologic structure (dip slopes/daylighted bedding planes). It also includes questionable landslides. (2) SUBAREA 4-2 includes the landslides mapped in the present study and nearby unstable areas.
[Recommended Application: Detailed, comprehensive engineering geological investigations, including specific slope-hazard mitigation measures, are necessary for any proposed development in Area 4 because slopes are unstable. Special Note: When determining land-use suitability, due to the highly unstable nature of terrain in Area 4, it is advisable to consider choosing one of two extreme alternatives and avoid intermediate approaches. For example, either the land should remain undeveloped or minimally developed and used as open space (nature preserve, park, golf course,etc.) or high density/high value development should be permitted that justifies the high cost of mitigation and occupies sufficient area to allow use of proper stabilization measures.]
This proves that the city fathers always knew this was a very dangerous area to build homes yet, because of graft and perks, they went ahead, citizens be damned!