Horizontal Earth movement in the Baldwin Hills, Los Angeles Area

Since subsidence is often accompanied by horizontal earth movements, an area undergoing vertical surveillance can be checked for such horizontal movement by triangulation if prior geodetic positions are known within the region. Triangulation station Baldwin Aux., whose position was determined by the 1934 Cooperative Control Survey of the metropolitan Los Angeles area, and which falls within a known area of subsidence, was reobserved. By using as control some of the other original 1933 stations which were external to the subsidence area, the adjustment resulting from observations on these points showed a horizontal movement of greater than 2 feet in 27 years. From secondary triangulation emanating from the 1961 position of Baldwin Aux., the horizontal movement of other previously positioned points was determined, and resulting movement vectors were computed. Recommendations are made for a systematic program of reobservations to be made in the future. This program should follow the pattern of observing procedure and reduction that has been used so successfully in the past in the Terminal Island‐Long Beach subsidence area.