Slopes with apparently well-established vegetation can still fail. Examination of these failure areas indicates a concentration of surface roots and little or no significant roots below about three to four feet. In areas of manufactured slopes, current development practices dictate landscape including trees be established, irrigated, and maintained.

The practice of irrigation needed for the survival of the groundcover species promotes the development of near surface tree roots. Thus, a slope may have the appearance of well-established vegetation with associated low risk of surficial failure, but without a well-established, deep root system, the risk of surficial instability will remain relatively unchanged.